Immobilized selenium, a method of making, and uses of immobilized selenium in a rechargeable battery

ABSTRACT

An immobilized selenium body, made from carbon and selenium and optionally sulfur, makes selenium more stable, requiring a higher temperature or an increase in kinetic energy for selenium to escape from the immobilized selenium body and enter a gas system, as compared to selenium alone. Immobilized selenium localized in a carbon skeleton can be utilized in a rechargeable battery. Immobilization of the selenium can impart compression stress on both the carbon skeleton and the selenium. Such compression stress enhances the electrical conductivity in the carbon skeleton and among the selenium particles and creates an interface for electrons to be delivered and or harvested in use of the battery. A rechargeable battery made from immobilized selenium can be charged or discharged at a faster rate over conventional batteries and can demonstrate excellent cycling stability.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.15/434,655 filed Feb. 16, 2017, which is a continuation-in-part of U.S.patent application Ser. No. 15/262,407 filed Sep. 12, 201.6, whichclaims the benefit of Chinese patent application no. 201510608018.4,filed Sep. 22, 2015, the disclosure of each of which is incorporated.herein by reference in its entirety. This application also claims thebenefit of US Provisional Application Nos. 62/367,314, filed Jul. 27,2016; 62/364,113, filed Jul. 19, 2016; and 62/296,286, filed Feb. 17,2016, the disclosure of each of which is also incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present application relates to the field of lithium secondarybatteries of high energy density. More particularly, the applicationrelates to a method of preparing carbon-selenium nanocomposite materialsand their applications. The present invention also relates toimmobilized selenium comprising selenium and carbon. It also relates toa method of making and the utility of the immobilized selenium. One ofthe uses of the immobilized selenium is in a rechargeable battery. Thepresent invention also relates to a rechargeable battery that canperform discharge-charge cycling at a fast rate (e.g., 10C-rate) with aminimum level of capacity fading while being able to substantiallyrecover its electrochemical performance, such as specific capacity, whencharged at a low rate such as at 0.1C-rate.

Description of Related Art

With the increasing human demand for energy, secondary batteries withhigh mass specific energy and high volumetric energy density, such aslithium-sulfur batteries and lithium-selenium batteries, have attractedwidespread interests. Group 6A elements in the Periodical Table, such assulfur and selenium, have shown two-electron reaction mechanisms in theelectrochemical reaction process with lithium. Despite the theoreticalmass specific capacity of selenium (675 mAh/g) being lower than that ofsulfur (1675 mAh/g), selenium has a higher density (4.82 g/cm³) thansulfur (2.07 g/cm³) Therefore the theoretical volumetric energy densityof selenium (3253 mAh/cm³) is close to the theoretical volumetric energydensity of sulfur (3467 mAh/cm³). At the same time, as compared withsulfur, which is close to an electrically insulating material, seleniumis semi-conductive electrically and shows better electrical conductiveproperties. Therefore, as compared to sulfur, selenium can demonstrate ahigher level of activity and better utilization efficiency even at ahigher loading level, leading to high energy and power density batterysystems. Moreover, a selenium-carbon composite can have a furtherimprovement in the electrical conductivity over sulfur-carbon compositeto obtain a higher activity electrode material.

As described in patent publication no. CN 104393304A, by passinghydrogen selenide gas through a graphene dispersion solution, thesolvent heat reduces the graphene oxide into graphene while oxidizes thehydrogen selenide into selenium. The thus prepared selenium grapheneelectrode material pairs with an ether electrolyte system, 1.5M lithiumbi-trifluoromethane sulfonimide (LiTFSI)/1,3-dioxolane (DOL) dimethylether (DME) (volume ratio 1:1); the charging specific capacity reaches640 mAh/g (approaching selenium theoretical specific capacity) in thefirst cycle. But in the charge-discharge process, polyselenide ionsdissolve in the electrolyte, showing significant amounts of the shuttleeffect, which causes the subsequent capacity decay. At the same tune,the procedures for preparing the graphene oxide raw material that isused in this process are complicated, not suitable for industrialproduction.

Patent CN104201389B discloses a lithium-selenium battery cathodematerial, utilizing a nitrogen-containing layered porous carboncomposite current-collector which was compounded with selenium. Inpreparing the nitrogen-containing layered porous carbon compositecurrent collector, nitrogen-containing conductive polymer is firstdeposited or grown on the surface of a piece of paper, followed byalkali activation and high temperature carbonization, resulting in anitrogen-containing layered porous carbon composite current collectorwith carbon fiber as network structure that supports itself; and suchnitrogen-containing layered porous carbon composite current collector isthen further compounded with selenium. The deposition method forpreparing a conductive polymer is complicated and the process for filmformation or growth is hard to control. The preparation process iscomplicated, which associates with undesirably high costs.

Moreover, the demand for a long life, high-energy-density andhigh-power-density rechargeable battery with the ability of beingcharged and discharged at a fast rate is ever increasing in electronics,electric/hybrid vehicles, aerospace/drones, submarines, and otherindustrial, military, and consumer applications. Lithium ion batteriesare examples of rechargeable batteries in the above-mentionedapplications. However, the need for better performance and cyclingcapability have not been filled with lithium ion batteries as thetechnology in lithium ion battery has matured.

Atomic oxygen has an atomic weight 16 and has a capability for 2electron transfers. A lithium-oxygen rechargeable battery has beenstudied for the purpose of making high energy density batteries. When abattery involves an oxygen cathode that pairs with lithium or sodiummetal as an anode, it has the greatest stoichiometric energy density.However, a majority of technical problems in the Li//Na-Oxygen batteryremains unresolved.

Elemental sulfur is also in the oxygen group and has the second highestenergy density (after oxygen) when paired with a lithium or sodium metalanode. A lithium-sulfur or sodium-sulfur battery has been widelystudied. However, polysulfide ions (intermediates) that form during theLi—S or Na—S battery discharging process dissolve in the electrolyte andshuttle from cathode to anode. Upon reaching the anode, polysulfideanions react with lithium or sodium metal, resulting in a loss of energydensity, which is undesirable for a battery system. In addition, sulfuris an insulator, which requires a high loading level of carbon materialsto achieve a minimum level of electrical conductivity. Due to theextremely low electrical conductivity of sulfur, a Li/Na—S rechargeablebattery is very difficult to discharge or charge at a fast rate.

SUMMARY OF THE INVENTION

Disclosed herein is a process to prepare a two-dimensional carbonnanomaterial, which has a high degree of graphitization. Thetwo-dimensional carbon nanomaterials are compounded with selenium toobtain a carbon-selenium composite material, which is used as a cathodematerial that pairs with anode material containing lithium, resulting ina lithium-selenium battery that has a high energy density and stableelectrochemical performances. A similar process can be used to furtherassemble a pouch cell, which also demonstrates excellent electrochemicalproperties.

Also disclosed is a method to prepare selenium-carbon composite materialwith readily available raw materials and simple preparation procedures.

The selenium-carbon composite material described herein can be obtainedfrom a preparation method that comprises the following steps:

(1) Carbonize alkali metal organic salts or alkaline earth metal organicsalts in high temperature, and then wash with dilute hydrochloric acidor some other acids, and dry to obtain a two-dimensional carbonmaterial;

(2) Mix the two-dimensional carbon material obtained in step (1) withselenium in organic solution, heat and evaporate the organic solvent,and then achieve compounding selenium with the two-dimensional carbonmaterial through a multi-stage heat ramping and soaking procedure toobtain carbon-selenium composite.

In step (1), the alkali metal organic salt can be selected from one orseveral of potassium citrate, potassium gluconate, and sucrose acidsodium. The alkaline earth metal organic salt can be selected from oneor both of calcium gluconate, and sucrose acid calcium. The hightemperature carbonization can be performed at 600-1000° C., desirably,700-900° C.; carbonation time for 1-10 hours, desirably for 3-5 hours.

In step (2), the organic solvent can be selected from one or several ofethanol, dimethylsulfoxide (DMSO), toluene, acetonitrile,N,N-dimethylformamide (DMF), carbon tetrachloride, and diethyl ether orethyl acetate; multi-stage heat ramping and soaking section can bereferred as to a ramping rate 2-10° C./min, desirably 5-8° C./min, to atemperature between 200 and 300° C., desirably between 220 and 280° C.,followed by soaking at the temperature for 3-10 hours, desirably, 3-4hours; then continue to heat up to 400-600° C., desirably, 430-460° C.,followed by soaking for 10-30 hours, desirably 15-20 hours.

Also disclosed herein is a lithium-selenium secondary battery thatcomprises the carbon-selenium composite materials. The lithium-seleniumsecondary battery can further include: a lithium-containing anode, aseparator, and an electrolyte.

The lithium-containing anode may be one or several of lithium metal, alithiated graphite anode, and lithiated silicon carbon anode materials(through assembling the graphite and silicon-carbon anode materials andlithium anode into a half cell battery, discharge to prepare lithiatedgraphite anode and lithiated silicon-carbon anode materials). Theseparator (membrane) can be a commercially available membrane, such as,without limitation, a Celgard membrane, a Whatman membrane, a cellulosemembrane, or a polymer membrane. The electrolyte can be one or severalof a carbonate electrolyte, an ether electrolyte, and ionic liquids.

The carbonate electrolyte can be selected from one or several fromdiethyl carbonate (DEC), dimethyl carbonate (DMC), ethylene carbonate(EC), ethyl methyl carbonate (EMC), and propylene carbonate (PC); andthe solute can be selected from one or several from lithium hexafluorophosphate (LiPF₆), lithium bis(trifluoromethanesulfonyl) imide (LiTFSI),lithium perchlorate (LiClO₄) and lithium bis(fluorosulfonyl) imide(LiFSI).

For the ether electrolytic solution, the solvent can be selected one orseveral from 1,3-dioxolane (DOL), ethylene glycol dimethyl ether (DME)and triethylene glycol dimethyl ether (TEGDME); and the solute can beselected in one or more from lithium hexafluorophosphate (LiPF₆),lithium bis-(trifluoromethanesulfonyl) imide (LiTFSI), lithiumperchlorate (LiClO₄) and lithium bis-fluorosulfonylimide (LiFSI).

For ionic liquids, the ionic liquid can be one or more room temperatureionic liquid [EMIm] NTf2 (1-ethyl-3-methylimidazolium histrifluoromethane sulfonimide salt), [Py13] NTf2(N-Propyl-N-methylpyrrolidine his trifluoromethane sulfonimide salt),[PP13] NTf2 (N-propyl-methylpiperidine alkoxy-N-Bis trifluoromethanesulfonimide salts); and the solute can be selected in one or more fromlithium hexafluorophosphate (LiPF₆), bis(trifluoromethylsulfonyl) imide(LiTFSI), lithium perchlorate (LiClO₄) and lithium bisfluorosulfonylimide (LiFSI).

Also described herein is a lithium-selenium pouch cell battery thatincludes the carbon selenium composite material.

Compared to the prior art, with respect to the method for preparingselenium carbon composite material disclosed herein, the two-dimensionalcarbon material has the advantages that the raw materials are readilyavailable at low cost, the preparation method is simple, highlypractical and suitable for mass production, and the obtained seleniumcarbon composite material exhibits excellent electrochemical properties.

Also disclosed herein is immobilized selenium (an immobilized seleniumbody) comprising selenium and a carbon skeleton. The immobilizedselenium comprises at least one of the following: (a) requires gainingenough energy for a selenium particle to reach a kinetic energy of ≥9.5kJ/mole, ≥9.7 kJ/mole, ≥9.9 kJ/mole, ≥10.1 kJ/mole, ≥10.3 kJ/mole, or≥10.5 kJ/mole to escape the immobilized selenium system; (b) atemperature of 490° C. or higher, ≥500° C., ≥510° C., ≥520° C., ≥530°C., ≥540° C., ≥550° C., or ≥560° C. is required for selenium particlesto gain enough energy to escape the immobilized selenium system; (c) thecarbon skeleton has a surface area (with pores less than 20 angstroms)≥500 m²/g, ≥600 m²/g, ≥700 m²/g, ≥800 m²/g, ≥900 m²/g, or ≥1,000 m²/g;(d) the carbon skeleton has a surface area (for pores between 20angstroms and 1000 angstroms) 20% or less, 15% or less, 10% or less, 5%or less, 3% or less, 2% or less, 1% or less of the total surface area.

Also disclosed herein is a cathode or a rechargeable battery comprisingimmobilized selenium. The selenium may be doped with other elements,such as, but not limited to, sulfur.

Also disclosed herein is a composite including selenium and carboncomprising platelet morphology with as aspect ratio of ≥1, ≥2, ≥5, ≥10,or ≥20.

Also disclosed herein is a cathode including a composite comprisingselenium and carbon and comprising platelet morphology with an aspectratio of ≥1, ≥2, ≥5, ≥10, or ≥20. Also disclosed herein is arechargeable battery including a composite comprising selenium andcarbon and comprising platelet morphology with the foregoing aspectratio.

Also disclosed herein is a rechargeable battery comprising a cathode, ananode, a separator, and an electrolyte. The rechargeable battery can becharged at 0.1C, 0.2C, 0.5C, 1C, 1.5C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C,10C or faster. The cathode can comprise at least one element of achalcogen group such as selenium, sulfur, tellurium, and oxygen. Theanode can comprise at least one element of an alkali metal, alkali earthmetals, and a group IIIA metal or metals. The separator can comprise anorganic separator or an inorganic separator whose surface can optionallybe modified. The electrolyte can comprise at least one element of alkalimetals, alkali earth metals, and a group IIIA metal or metals. Thesolvent in the electrolyte solution can comprise organic solvents,carbonate-based, ether-based, or ester-based.

The rechargeable battery may have a specific capacity of 400 mAh/g orhigher, 450 mAh/g or higher, 500 mAh/g or higher, 550 mAh/g or higher,or 600 mAh/g or higher. The rechargeable battery may be able to undergoelectrochemical cycling for 50 cycle or more, 75 cycles or more, 100cycles or more, 200 cycles or more, etc. The rechargeable battery mayretain a battery specific capacity greater than 30%, greater than 40%,greater than 50%, greater than 60%, greater than 70%, or greater than80% of the 2^(nd) discharge specific capacity at a cycling rate of 0.1Cafter conducting high C-Rate charge-discharge cycling (e.g., 5 cycles at0.1C, 5 cycles at 0.2C, 5 cycles at 0.5C, 5 cycles at 1C, 5 cycles at2C, 5 cycles at 5C, and 5 cycles at 10C). The rechargeable battery mayhave a Coulombic efficiency ≥50%, ≥60%, ≥70%, ≥80%, or ≥90%. Therechargeable battery can be used for electronics, an electric or hybridvehicle, an industrial application, a military application such as adrone, an aerospace application, a marine application, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a 50,000× scanning electron microscope photograph of thecarbon material of Example 1;

FIG. 2 is a 0.1C charge and discharge curve of the lithium seleniumbattery of Example 1;

FIG. 3 is a 0.1C charge and discharge curve of the lithium seleniumbattery of comparative Example 2;

FIG. 4 is a schematic illustration of the pouch cell battery of Example1;

FIG. 5 is a 0.05C charge and discharge curve of the pouch cell batteryof Example 1;

FIG. 6 is a flow diagram of a process of making immobilized selenium;

FIG. 7 is a scanning electron microscope image of a carbon skeletonprepared by the process of Example 9;

FIG. 8 is X-ray diffraction patterns for the carbon skeleton prepared bythe process of Example 9;

FIG. 9 is Raman spectrum of the carbon skeleton that was prepared by theprocess of Example 9;

FIG. 10A is a graph of cumulative and incremental surface area for thecarbon skeleton prepared by the process of Example 9;

FIG. 10B is a graph of cumulative and incremental pour volumes for thecarbon skeleton prepared by the process of Example 9;

FIG. 11A is a graph of TGA analysis for the immobilized selenium thatwas prepared by the process of Example 10;

FIG. 11B is a graph of TGA analysis for non-immobilized selenium samplesprepared by the process of Example 10 using Se-Super P carbon andSe-graphite;

FIG. 11C is a graph of TGA analysis of the non-immobilized seleniumsample prepared using the Se-Super P carbon (FIG. 11B) under a flow ofargon gas and at heating rates of 16° C./min and 10° C./min;

FIG. 11D is a graph of rate constants for non-immobilized selenium(Se-Super P composite-solid line), and 2 different samples ofimmobilized selenium (228-110 (dotted line) and 115-82-2 (dashed line))prepared by the process of Example 10;

FIG. 12 is a graph of Raman spectrum of the immobilized seleniumprepared by the process of Example 10;

FIG. 13 is a graph of X-ray diffraction patterns for the immobilizedselenium prepared by the process of Example 10;

FIG. 14 is an SEM image of the immobilized selenium prepared by theprocess of Example 10;

FIG. 15 is an exploded view of a coin cell battery including a cathodeprepared according to the process of Example 11 or Example 13;

FIG. 16 are graphs of cycling test results for a first lithium-seleniumcoin cell battery (0.1C) (FIG. 16A—left) and a second lithium-seleniumcoin cell battery (0.1C and then 1C) (FIG. 16A—right) of the type shownin FIG. 15 that were prepared by the process of Example 12;

FIG. 17 are graphs of cycling tests for a lithium-selenium coin cellbattery of the type shown in FIG. 15 that was prepared by the process ofExample 12 at different cycling rates;

FIG. 18 are graphs of 0.1C cycling test results for alithium-sulfur-doped-selenium coin cell battery of the type shown inFIG. 15 made in accordance with Example 13 with a polymer separator; and

FIG. 19 are graphs of 1C cycling test results for alithium-sulfur-doped-selenium coin cell battery of the type shown inFIG. 15 made in accordance with Example 13 with a polymer separator.

DESCRIPTION OF THE INVENTION

In conjunction with the specific examples, the present invention will befurther described below. Unless otherwise specified, the experimentalmethods in the following examples are all conventional; the reagents andmaterials are all available from commercial sources.

Example 1

(A) Preparation of Selenium Carbon Composite Material

After grinding and milling, an appropriate amount of potassium citrateis calcined at 800° C. for 5 hours under an inert atmosphere, and cooledto room temperature. Washed with dilute hydrochloric acid to a neutralpH; filtered and dried to give a two-dimensional carbon nanomaterial(FIG. 1); according to the mass ratio of 50:50, weigh the twodimensional carbon material and selenium, and then stir and mix with theethanol solution of selenium uniformly; after solvent evaporation, drythe mixture in dry oven; the dried mixture was heated at 5° C./min to240° C. and soaked for 3 hours; then continues to heat up at 5° C./reinto 450° C.; soaked for 2.0 hours; cooled to room temperature, whichresulted in the selenium carbon composite material.

(B) Preparation of the Selenium Carbon Composite Cathode

The above-prepared selenium carbon composites are mixed with carbonblack Super P (TIMCAL) and binder CMC/SBR (weight ratio 1:1) along withwater by a fixed formulation by pulping, coating, drying and otherprocedures to obtain a selenium carbon composite cathode.

(C) Assembling Lithium—Selenium Battery

The above-prepared selenium carbon composite cathode, lithium foil asanode, Celgard diaphragm as separator and 1M LiPF₆ in EC/DMC as theelectrolyte were assembled into a lithium selenium coin cell battery anda lithium selenium pouch cell battery, a schematic illustration of whichis provided in FIG. 4.

(D) Lithium-Selenium Battery Test

Use a charge-discharge apparatus to perform a constant current chargedischarge test on the lithium-selenium coin cell battery and lithiumselenium pouch cell battery. Test voltage range is between 1.0 and 3.0 Vand test temperature is 25° C. Discharge specific capacity and the levelof charge-discharge current are standardly calculated based on the massof selenium. The charge-discharge current is 0.1C or 0.05C. The lithiumselenium coin charge and discharge curve is shown in FIG. 2, thespecific test results are shown in Table 1 below. Lithium selenium pouchcell test results are shown in FIG. 5.

Example 2

Conditions are the same as in Example 1, with the exception that the rawmaterial carbonized for two-dimensional carbon is sodium citrate.Battery test results are summarized in Table 1 below.

Example 3

Conditions are the same as in Example 1, with the exception that the rawmaterial carbonized for two-dimensional carbon is potassium gluconate.Battery test results are summarized in Table 1 below.

Example 4

Conditions are the same as in Example 1, with the exception that thehigh-temperature carbonization temperature for the carbon material is650° C. Battery test results are summarized in Table 1 below.

Example 5

Conditions are the same as in Example 1, with the exception that thedried mixture was heated at 5° C./min to 300 and soaked at thistemperature for 3 hours. Battery test results are summarized in Table 1below.

Example 6

Conditions are the same as in Example 1, with the exception that thedried mixture was heated at 5° C./min to 240° C. and soaked at thistemperature for 3 hours, then continued to heat up to 600° C., andsoaked at this constant temperature for 20 hours. Battery test resultsare summarized in Table 1 below.

Example 7

Conditions are the same as in Example 1, with the exception that thelithium-Se battery is packed with lithiated graphite anode, instead ofthe lithium anode sheet. Battery test results are summarized in Table 1below.

Example 8

Conditions are the same as in Example 1, with the exception that thelithium-Se battery is packed with lithiated silicon carbon anode,instead of the lithium anode sheet. Battery test results are summarizedin Table 1 below.

Comparative Example 1

Conditions are the same as in Example 1, with the exception that the useof polyacrylonitrile as the raw material. Battery test results aresummarized in Table 1 below.

Comparative Example 2

Conditions are the same as in Example 1; with the exception that aone-step compound method is used to prepare the selenium and carboncomposite. In this example, the dried selenium carbon mixture was heatedat 5° C./min to 500° C. and soaked at this temperature for 23 hours toobtain selenium carbon composite material. The charge-discharge curve ofa battery made from the thus obtained selenium carbon composite materialis shown in FIG. 3; the battery test results are summarized in Table 1below.

Table 1 Summarized Battery Test Results

The first cycle discharge The first cycle charge capacity capacity/thefirst cycle The 50^(th) cycle Numbering (mAh/g) discharge capacity (%)capacity (mAh/g) Example 1 1,050 78.1 756 Example 2 940 74.6 672 Example3 962 75.3 683 Example 4 987 72.1 680 Example 5 936 73.2 653 Example 6972 70 661 Example 7 836 72.5 580 Example 8 910 73 600 Comparative 63555 350 Example 1 Comparative 980 40.8 386 Example 2

Having thus described a method of preparing a selenium carbon compositematerial, a method of making immobilized selenium and the use of theimmobilized selenium, e.g., in a rechargeable battery, will bedescribed.

Selenium is an element in the same group as oxygen and sulfur namely,Group 6 of the Periodic Table of the elements. Selenium may beadvantageous over oxygen and sulfur in term of its substantially highelectrical conductivity. US 2012/0225352 discloses making Li-seleniumand Na-selenium rechargeable batteries, with good capacity and cyclingcapability. However, a certain level of polyselenide anions shuttlebetween the cathodes and anodes of such batteries, resulting inadditional electrochemical performances that need to be substantiallyimproved for practical uses. Literature relevant to this field includesthe following:

-   “Electrode Materials for Rechargeable Batteries”, Ali Aboulmrane and    Khalil Amine, US Patent Application 2012/0225352, Sep. 6, 2012.-   “Lithium-Selenium Secondary Batteries Having non-Flammable    Electrolyte”, Hui He, Bor Z. Jang, Yanbo Wang, and Aruna Zhamu, US    Patent Application 2015/0064575, Mar. 5, 2015.-   “Electrolyte Solution and Sulfur-based or Selenium-based Batteries    including the Electrolyte Solution”, Fang Dai, Mei Cai, Qiangfeng    Xiao, and Li Yang, US Patent Application 2016/0020491, Jan. 21,    2016.-   “A New Class of Lithium and Sodium Rechargeable Batteries Based on    Selenium and Selenium-Sulfur as a Positive Electrode”, Ali    Abouimrane, Damien Dambournet, Kerena W. Chapman, Peter J. Chupa,    Wei Wang, and Khalil Amine, J. Am. Chem. Soc. 2012, 134, 4505-4508.

“A Free-Standing and Ultralong-life Lithium-Selenium Battery CathodeEnabled by 3D Mesoporous Carbon/Graphene Hierachical Architecture”, KaiHan, Zhao Liu, Jingmei Shen, Yuyuan Lin, Fand Dai, and Hongqi Ye, Adv.Funct. Mater., 2015, 25, 455-463.

“Micro- and Mesoporous Carbide-Derived Carbon-Selenium Cathodes forHigh-Performance Lithium Selenium Batteries”, Jung Tai Lee, Hyea Kim,Marin Oschatz, Dong-Chan Lee, Feixiang Wu, Huan-Ting Lin, Bogdan Zdyrko,Wan Il Chao, Stefan Kaskel, and Gleb Yushin, Adv. Energy Mater. 2014,1400981.

-   “High-Performance Lithium Selenium Battery with Se/Microporous    Carbon Composite Cathode and Carbonate-Based Electrolyte”, Chao Wu,    Lixia Yuan, Zhen Li, Ziqi Yi, Rui Zeng, Yanrong Li, and Yunhui    Huang, Sci. China Mater. 2015, 58, 91-97.-   “Advanced Se—C Nanocomposites: a Bifunctional Electrode Material for    both Li—Se and Li-ion Batteries”, Huan Ye, Ya-Xia Yin, Shuai-Feng    Zhang, and Yu-Guo Guo, J. Mater. Chem. A., May 23, 2014.-   “Lithium Iodide as a Promising Electrolyte Additive for    Lithium-Sulfur Batteries: Mechanisms of Performance Enhancement”,    Feixiang Wu, Jung Tae Lee, Naoki Nitta, Hyea Kim, Oleg Borodin, and    Gleb Yushin, Adv. Mater. 2015, 27, 101-108.-   “A Se/C Composite as Cathode Material for Rechargeable Lithium    Batteries with Good Electrochemical Performance”, Lili Li, Yuyang    Hou, Yaqiong Yang, Minxia Li, Xiaowei Wang, and Yuping Wu, RSC Adv.,    2014, 4, 9086-9091.-   “Elemental Selenium for Electrochemical Energy Storage”, Chun-Peng    Yang, Ya-Xia Yin, and Yu-Guo Guo, J. Phys. Chem. Lett. 2015, 6,    256-266.-   “Selenium@mesoporous Carbon Composite with Superior Lithium and    Sodium Storage Capacity”, Chao Luo, Yunhua Xu, Yujie Zhu, Yihang    Liu, Shiyou Zheng, Ying Liu, Alex Langrock, and Chunsheng Wang,    ACSNANO, Vol. 7, No. 9, 8003-8010.

Also disclosed herein is immobilized selenium comprising selenium andcarbon. Immobilized selenium may comprise elemental form selenium orcompound form selenium. Selenium may be doped with other element, suchas, but not limited to, sulfur. The immobilized selenium enables thelocalization of elemental selenium atoms which functionelectrochemically properly without being shuttled between a cathode andan anode of a battery. Immobilization of selenium allows an elementalselenium atom to gain two electrons during a discharge process and toform a selenide anion at the location where the selenium molecule/atomis immobilized. The selenide anion can then give up two electrons duringa charging process to form an elemental selenium atom. Therefore,immobilized selenium can work as an electrochemical active agent for arechargeable battery that has a specific capacity that may be up to astoichiometric level, can have a Coulombic efficiency that may be ≥95%,≥98%, or as high as 100%, and can achieve a substantially-improvedsustainable cycling capability.

In a battery made with immobilized selenium the electrochemicalbehaviors of elemental selenium atoms and selenide anions duringcharging are processes that desirably function properly. Carbonskeletons possessing Sp² carbon-carbon bonds have delocalized electronsdistributed over a conjugated six-member-ring aromatic π-bonds acrossG-band graphene-like local networks that are bounded by D-band carbon.In the presence of an electrical potential, such delocalized electronsmay flow with little or no electrical resistance across the carbonskeleton. Selenium immobilization can also compress a carbon skeleton'sSp² carbon-carbon bonds, resulting in stronger carbon-carbon bonds,possibly leading to improved electron conductivity within the carbonskeleton network. At the same time, selenium immobilization may alsolead to compression of selenium particles, resulting in strongerselenium-selenium chemical and physical interactions, possibly leadingto improved electrical conductivity among immobilized seleniumparticles. When both carbon-carbon bonds and Se—Se bonds are enhanceddue to selenium immobilization, carbon-selenium interactions are alsoenhanced by the compression in addition to the presence of a stabilizedselenium portion to which carbon skeleton can bond. This portion of theselenium may act as an interface layer for a carbon skeleton tosuccessfully immobilize the stabilized selenium portion. Therefore,electrons may flow with a minimal electrical resistance between thecarbon skeleton and the immobilized selenium, whereupon theelectrochemical charge/discharge processes may function efficiently in arechargeable battery. This, in turn, allows the rechargeable battery tomaintain a near-stoichiometric specific capacity and have the capabilityof cycling at almost any practical rate with a low level of damage tothe electrochemical performance of the battery.

A carbon skeleton may be porous and may be doped with anothercomposition. The pore size distributions of the carbon skeleton mayrange between sub angstrom to a few microns or to a pore size that apore size distribution instrument can characterize by using nitrogen,argon, CO₂ or other absorbent as a probing molecule. The porosity of thecarbon skeleton may comprise a pore size distribution that peaks in therange of at least one of the following: between sub-angstrom and 1000angstroms, or between one angstrom and 100 angstroms, or between oneangstrom and 50 angstroms, or between one angstrom and 30 angstroms, andor between one angstrom and 20 angstroms. The porosity of the carbonskeleton may further comprise pores having a pore size distribution withmore than one peak in the ranges described in the previous statement.Immobilized selenium may favor carbon skeleton having small pore sizesin which electrons may be delivered and harvested quickly with minimumelectrical resistance, which may allow the selenium to function moreproperly electrochemically in a rechargeable battery. The small poresize may also provide more carbon skeleton surface area where the firstportion of the selenium can form a first interface layer for a secondportion of selenium immobilization. In addition, the presence in acarbon skeleton having a certain portion of medium size pores and acertain portion of large size pores may also be beneficial for effectivedelivery of solvent lithium ions from bulk solvent media to a small poreregion where lithium ions may lose coordinated solvent molecules and gettransported in solid phase of lithium selenide.

The pore volume of the carbon skeleton may be as low as 0.01 mL/g andmay be as much as 5 mL/g, or may be between 0.01 mL/g and 3 mL/g, or maybe between 0.03 mL/g and 2.5 mL/g, or may be between 0.05 mL/g and 2.0mL/g. The pore volume having pore sizes less than 100 angstroms, or lessthan 50 angstrom, or less than 30 angstroms, or less than 20 angstromsmay be greater than 30%, or greater than 40%, or greater than 50%, orgreater than 60%, or greater than 70%, or greater than 80% of the totalmeasurable pore volume that can be measured by using a BET instrumentwith nitrogen, CO₂, argon, and other probing gas molecules. The BETdetermined surface area of the carbon may be greater than 400 m²/g, orgreater than 500 m²/g, or greater than 600 m²/g, or greater than 700m²/g, or greater than 800 m²/g, or greater than 900 m²/g, or greaterthan 1000 m²/g.

The carbon may also be substantially amorphous, or it may have acharacteristic of a very broad peak centered at a d-spacing around 5angstroms.

The carbon may comprise Sp² carbon-carbon bonds, having Raman peakshifts featuring a D-band and a G-band. In an example, Sp² carbon-carbonbonds of the carbon feature a D-band centered at 1364±100 cm⁻¹ with aFWHM about 296±50 cm⁻¹ and a G-band center at 1589±100 cm⁻¹ with a FWHMabout 96±50 cm⁻¹ in Raman spectrum. The ratio of the area of D-band toG-band may range from 0.01 to 100, or from 0.1 to 50, or from 0.2 and20.

The carbon may be of any morphology, namely, for example, platelet,sphere, fiber, needle, tubular, irregular, interconnected, agglomerated,discrete, or any solid particles. Platelet, fiber, needle, tubular, orsome morphology having a certain level of aspect ratio may be beneficialfor achieving better inter-particle contact, resulting in betterelectrical conductivity, possibly enhancing rechargeable batteryperformance.

The carbon may be of any particle size, having a median particle sizefrom a nanometer to a few millimeters, or from a few nanometers to lessthan 1000 microns, or from 20 nm to 100 microns.

The property of a carbon skeleton can affect selenium immobilization andinteractions between the carbon skeleton surface and selenium particlescan affect the performance of a rechargeable battery. The location ofSp² carbon in a carbon skeleton can aid in achieving Se immobilization.Sp² carbon from small carbon skeleton pores may be favored, which can bequantified by NLDFT surface area method, as discussed in the Example 9herein. The surface area from carbon skeleton pores less than 20angstroms may be ≥500 m²/g, ≥600 m²/g, ≥700 m²/g, ≥800 m²/g, ≥900 m²/g,or ≥1,000 m²/g. The surface areas from the carbon skeleton pores between20 angstroms and 1000 angstroms may be 20% or less, 15% or less, 10% orless, 5% or less, 3% or less, 2% or less, or 1% or less of the totalsurface area of the carbon skeleton.

Immobilized selenium can comprise selenium that vaporizes at atemperature higher than elemental selenium, referring to the followingdefinition of selenium vaporization: Elemental selenium in a Se-Super Pcomposite loses 50% of its weight at a temperature of 480° C.; elementalselenium in a Se/Graphite composite loses its weight by 50% of thecontained selenium at a temperature of 471° C. Immobilized seleniumloses 50% of its weight at a temperature higher than 480° C., forexample at a temperature ≥490° C., ≥500° C., ≥510° C., ≥520° C., ≥530°C., ≥540° C., ≥550° C., ≥560° C., ≥570° C., or ≥580° C. or more.Selenium in the immobilized selenium may need a kinetic energy of ≥9.5kJ/mole, ≥9.7 kJ/mole, ≥9.9 kJ/mole, ≥10.1 kJ/mole, ≥10.3 kJ/mole, or≥10.5 kJ/mole or more to overcome the bonding and or intermolecularforces in the immobilized selenium system and to escape to the gasphase. In an example, the last portion of the immobilized selenium thatvaporizes can require a kinetic energy of 11,635 joules/mole 660° C.) toescape the carbon skeleton and may be critical for seleniumimmobilization and may work as interfacial material between the carbonskeleton and the majority of the immobilized selenium molecules.Therefore, this portion of the selenium that requires a kinetic energyof 11,635 joules/mole is called interfacial selenium. The amount ofinterfacial selenium in the immobilized selenium may be ≥1.5%, ≥2.0%,≥2.5 or 3.0% of the total immobilized selenium.

Immobilized selenium can comprise selenium that has an activation energyhigher than that for conventional (non-immobilized) selenium to overcomein order for the selenium to escape from the immobilized Se—C compositesystem. The activation energy for non-immobilized selenium (Se-Super Pcomposite system) was determined to be about 92 kJ/mole according toASTM Method E1641-16. The activation energy for selenium in theimmobilized selenium comprising selenium and carbon is ≥95 kJ/mole, ≥98kJ/mole, ≥101 kJ/mole, ≥104 kJ/mole, ≥107 kJ/mole, or ≥110 kJ/mole. Theactivation energy for selenium in the immobilized selenium comprisingselenium and carbon is ≥3%, ≥6%, ≥9%, ≥12%, ≥15%, or ≥18% greater thanthat for selenium in Se-Super P composite. The immobilized selenium canbe more stable than non-immobilized selenium, which is the reason thatthe battery comprising immobilized selenium may cycle electrochemicallybetter, probably due to the minimization (or elimination) of seleniumshuttling between cathode and anode, resulting from selenium beingimmobilized in Se—C composite.

Immobilized selenium may comprise selenium that may be Raman-inactive orRaman-active, typically having a Raman peak at 255±25 cm⁻¹, or at 255±15cm⁻¹, or at 255±10 cm⁻¹. Raman relative peak intensity is defined as thearea of the Raman peak at 255 cm⁻¹ relative to the area of the D-bandpeak of the carbon Raman spectrum. Immobilized carbon may compriseselenium having a Raman relative peak intensity of ≥0.1%, ≥0.5%, ≥1%,≥3%, ≥5% Immobilized selenium may contain ≥5% selenium, ≥10% selenium,≥20% selenium, ≥30% selenium, ≥40% selenium, ≥50% selenium, ≥60%selenium, or ≥70% selenium.

Immobilized selenium can comprise selenium having a red shift from theRaman peak of pure selenium. A red shift is defined by a positivedifference between the Raman peak location for the immobilized seleniumand that for pure selenium. Pure selenium typically has a Raman peak atabout 235 cm⁻¹ Immobilized selenium can comprise selenium that has a redshift of the Raman peak by ≥4 cm¹, ≥6 cm¹, ≥8 cm⁻¹, ≥10 cm⁻¹, ≥12 cm⁻¹,≥14 cm⁻¹, or ≥16 cm⁻¹. A red shift in Raman peak suggests that there isa compression on the selenium particles.

Immobilized selenium can comprise carbon that may be under compression.Under compression, electrons can flow with a minimum resistance, whichfacilitates fast electron delivery to selenium and from selenium anionsfor electrochemical processes during discharge-charge processes for arechargeable battery. D-band and or G-band in Raman spectrum for the Sp²carbon-carbon bonds of the carbon skeleton comprising the immobilizedselenium may show a red shift, by ≥1 cm⁻¹, ≥2 cm⁻¹, ≥3 cm⁻¹, ≥4 cm⁻¹, or≥5 cm⁻¹.

Immobilized selenium comprises selenium that can have a higher collisionfrequency than non-immobilized selenium. Such high collision frequencymay result from selenium in the immobilized Se—C system that is undercompression. The collision frequency for selenium in non-immobilizedselenium was determined to be around 2.27×10⁵, according to the ATSMMethod E1641-16. The collision frequency for selenium in the immobilizedselenium comprising selenium and carbon is ≥2.5×10⁵, ≥3.0×10⁵, ≥3.5×10⁵,≥4.0×10⁵, ≥4.5×10⁵, ≥5.0×10⁵, ≥5.5×10⁵, ≥6.0×10⁵, or ≥8.0×10⁵. Theimmobilized selenium can have a higher collision frequency by ≥10%,≥30%, ≥50%, ≥80%, ≥100%, ≥130%, ≥150%, ≥180%, or ≥200% than that fornon-immobilized selenium in Se—C composite. This may lead to betterelectron conductivity in the immobilized selenium system because of morecollisions among selenium species. The immobilized selenium in Se—Ccomposite would also have a higher collision frequency against the wallof the carbon host (e.g., a carbon skeleton), which may result in abetter delivery or harvesting of electrons from the carbon skeletonduring electrochemical cycling, which can lead to a battery (comprisingimmobilized selenium) that has improved cycling performances, such asattaining more cycles and or cycling at a much higher C-rate, which ishighly desirable.

Immobilized selenium comprises selenium that has less tendency to leaveits host material (carbon), having a kinetic rate constant that is ≤1/5,≤1/10, ≤1/50, ≤1/100, ≤1/500, or ≤1/1000 of the kinetic rate constantfor non-immobilized/conventional selenium. In our example, immobilizedselenium comprises selenium that has less tendency to leave its hostmaterial (carbon), having a kinetic rate constant (at 50° C.) of≤1×10⁻¹⁰, ≤5×10⁻¹¹, ≤1×10⁻¹¹, ≤5×10⁻¹², or ≤5×10⁻¹³.

Immobilized selenium can comprise selenium that may be amorphous, asdetermined by X-ray diffraction measurements. A diffraction peak havinga d-spacing of about 5.2 angstroms is relatively smaller or weaker, forexample, 10% weaker, 20% weaker, 30% weaker, or 40% weaker, than thatfor the carbon skeleton.

Immobilized selenium may be prepared by physically mixing carbon andselenium followed by melting and homogenizing (or mixing or blending)selenium molecules to achieve selenium immobilization. The physicalmixing may be achieved by ball-milling (dry and wet), mixing with mortarand pestle (dry or wet), jet-milling, horizontal milling, attritionmilling, high shear mixing in slurries, regular slurry mixing withblade, etc. The physically mixed mixture of selenium and carbon may beheated at a temperature that is at or higher than the melting point ofselenium and below the melting temperature of carbon. The heating may becarried out in an inert gas environment such as, but not limited to,argon, helium, nitrogen, etc. The heating environment may comprise airor a reactive environment. Immobilization of selenium may be achieved byimpregnating dissolved selenium into carbon, followed by evaporation ofthe solvent. The solvent for dissolving selenium may comprise analcohol, an ether, an ester, a ketone, a hydrocarbon, a halogenatedhydrocarbon, a nitrogen-containing compound, a phosphorus containingcompound, a sulfur-containing compound, water, etc.

Immobilized selenium can be achieved by melting a large amount ofselenium in the presence of carbon, followed by removing extranon-immobilized selenium.

An immobilized selenium system or body may comprise immobilized selenium≥30%, ≥40%, ≥50%, ≥60%, ≥70%, ≥80%, or ≥90% of the total amount ofselenium in the system or body. The non-immobilized selenium canvaporize at a temperature lower than the immobilized selenium.

An immobilized selenium system or body may comprise immobilized seleniumthat is doped with one or more additional/other element(s) from Group 6of the Periodic Table, such as, for example, sulfur and/or tellurium.The dopant level may range from as low as 100 ppm by weight to as highas 85% of the weight of the immobilized selenium system or body.

An example process of making immobilized selenium is illustrated in FIG.6. In the process, selenium and carbon are mixed together (S1) under dryor wet conditions. The mixture can be optionally dried to a powder (S2)followed by optionally pelletizing the dried powder (S3). The results ofstep S1 and optionally steps S2 and S3 produce a carbon skeleton that isa starting material for step S4. In step S4, selenium is melted into thecarbon skeleton. The selenium melted into the carbon skeleton is allowedto dry thereby producing the immobilized selenium of step S5.Preparation and characterization of immobilized selenium will bedescribed later herein in connection with Example 10.

The immobilized selenium may be used as a cathode material for arechargeable battery. For making a cathode, the immobilized selenium maybe dispersed in a liquid media such as, but not limited to, water or anorganic solvent. The cathode comprising the immobilized selenium maycomprise a binder, optionally another binder, optionally anelectric-conductivity promoter, and an electric charge collector. Thebinder may be an inorganic or organic. An organic binder may be of anatural product, such as, for example, CMC, or a synthetic product, suchas, for example, a SBR Rubber latex. An electrical-conductivity promotercan be a type of carbon, such as, graphite-derived small particles,graphene, carbon nano-tubes, carbon nano-sheet, carbon blacks, etc. Anelectric charge collector may be, for example, an aluminum foil, acopper foil, a carbon foil, a carbon fabric, or other metallic foils.The cathode can be prepared by coating an immobilizedselenium-containing slurry (or slurries) onto the charge collector,followed by a typical drying process (air dry, oven-dry, vacuumoven-dry, etc.). The immobilized selenium slurry or slurries may beprepared by a high shear mixer, a regular mixer, a planetary mixer, adouble-planetary mixer, a ball mill, a vertical attritor, a horizontalmill, etc. The cathode comprising immobilized selenium may be pressed orroller-milled (or calendared) prior to its use in a battery assembly.

A rechargeable battery comprising immobilized selenium may comprise acathode comprising immobilized selenium, an anode, a separator, and anelectrolyte. The anode may comprise lithium, sodium, silicon, graphite,magnesium, tin, and/or and suitable and/or desirable element orcombination of elements from Group IA, Group IIA, Group IIIA, etc., ofthe periodic table of the elements (Periodic Table). The separator maycomprise an organic separator, an inorganic separator, or a solidelectrolyte separator. An organic separator may comprise a polymer suchas, for example, polyethylene, polypropylene, polyester, a halogenatedpolymer, a polyether, a polyketone, etc. An inorganic separator maycomprise a glass or quartz fiber, a solid electrolyte separator. Anelectrolyte may comprise a lithium salt, a sodium salt, or other salt, asalt of Group 1A of the Periodic Table, a salt of Group IIA of thePeriodic Table, and an organic solvent. The organic solvent may comprisean organic carbonate compound, an ether, an alcohol, an ester, ahydrocarbon, a halogenated hydrocarbon, a lithium containing-solvent,etc.

A rechargeable battery comprising immobilized selenium may be used forelectronics, an electric or hybrid vehicle, an industrial application, amilitary application such as a drone, an aerospace application, a marineapplication, etc.

A rechargeable battery comprising immobilized selenium may have aspecific capacity of 400 mAh/g active amount of selenium or higher, 450mAh/g or higher, 500 mAh/g or higher, 550 mAh/g or higher, or 600 mAh/gor higher. A rechargeable battery comprising immobilized selenium may beable to undergo electrochemical cycling for 50 cycle or more, 75 cyclesor more, 100 cycles or more, 200 cycles or more, etc.

A rechargeable battery comprising immobilized selenium may be able to becharged at 0.1C, 0.2C, 0.5C, 1C, 1.5 C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C,10C or faster. After conducting extensive high C-Rate charge-dischargecycling for 30 or more cycles (e.g., 5 cycles at 0.1C, 5 cycles at 0.2C,5 cycles at 0.5C, 5 cycles at 1C, 5 cycles at 2C, 5 cycles at 5C, and 5cycles at 10C), a rechargeable battery comprising immobilized seleniummay retain a battery specificcapacity >30%, >40%, >50%, >60%, >70%, >80% of the 2^(nd) dischargespecific capacity at a cycling rate of 0.1C.

Following are several examples to illustrate the spirit of theinventions. However, these examples should not be construed in alimiting sense.

Examples

Method of Characterization

Scanning Electron Microscopy (SEM) images were collected on a TescanVega scanning electron microscope equipped with an energy dispersiveanalysis X-Ray (EDX) detector.

Raman spectra were collected by a Renishaw inVia Raman Microscope(confocal). Laser Raman spectroscopy is widely used as a standard forthe characterization of carbon and diamond and provides readilydistinguishable signatures of each of the different forms (allotropes)of carbon (e.g., diamond, graphite, buckyballs, etc.). Combined withphotoluminescence (PL) technology, it offers a non-destructive way tostudy various properties of diamond including phase purity, crystal sizeand orientation, defect level and structure, impurity type andconcentration, and stress and strain. In particular, the width(full-width-half-maximum, FWHM) of the first order diamond Raman peak at1332 cm⁻¹, as well as the Raman intensity ratio between diamond peak andgraphitic peaks (D-band at 1350 cm⁻¹ and G-band at 1600 cm⁻¹), is adirect indicator of diamond and other carbon material quality.Furthermore, the stress and strain levels in diamond or other carbongrains and films can be estimated from diamond Raman peak shift. It hasbeen reported that the diamond Raman peak shift rate under hydrostaticstress is about 3.2 cm⁻¹/GPa, with the peak shifting to lower wavenumberunder tensile stress and higher wavenumber under compressive stress. TheRaman spectra discussed herein were collected using a Renishaw inViaRaman spectroscope with 514 nm excitation laser. More information aboutusing Raman spectroscopy to characterize diamond is also available inthe references (1) A. M. Zaitsev, Optical Properties of Diamond, 2001,Springer and (2) S. Prawer, R. J. Nemanich, Phil. Trans. R. Soc. Lond. A(2004) 362, 2537-2565.

The data for BET surface area and pore size distributions of carbonsamples were measured by nitrogen absorption and CO₂ absorption with a3Flex (Mircomeritics) equipped with a Smart VacPrep for sample degaspreparations. The sample is typically degased in Smart Vac-Prep at 250°C. for 2 hours under vacuum prior to CO₂ and N₂ absorption measurements.Nitrogen absorption is used to determine the BET surface area. Nitrogenabsorption data and CO₂ absorption data were combined to calculate poresize distributions of a carbon sample. For the details about combiningboth N₂ and CO₂ absorption data for determining the pore sizedistributions for carbon materials, please refer to “Dual gas analysisof microporous carbon using 2D-NLDFT heterogeneous surface model andcombined adsorption data of N₂ and CO₂”, Jacek Jagiello, Conchi Ania,Jose B. Parra, and Cameron Cook, Carbon 91, 2015, page 330-337.

The data for thermogravimetric analysis (TGA) and TGA-differentialscanning calorimetry (DSC) for immobilized selenium samples and thecontrol samples were measured by Netzsch Thermal Analyzer. The TGAanalysis was performed under an argon flow rate of ˜200 mL/min at aheating rate of 16° C./min, 10° C./min, 5° C./min, 2° C./min, 1° C./min,and other heating rates. For the purpose of consistency, a typicalamount of immobilized selenium sample used for TGA analysis was about 20mg.

Activation energy and collision frequency of the immobilized seleniumand non-immobilized selenium were determined by TGA following theprocedures described in ASTM Method E1641-16.

X-Ray diffraction results for different carbon, Se-carbon samples, andimmobilized selenium were collected on a Philip Diffractometer.

Battery cycling performances for rechargeable batteries comprisingimmobilized selenium were tested on Lanhe CT2001A Battery CyclingTester. Charge and discharge currents of the rechargeable batteriescomprising immobilized selenium were determined by the amount ofselenium contained in the immobilized selenium and cycling rate (0.1C,0.5C, 1C, 2C, 3C, 4C, 5C, 10C, etc.).

Example 9: Synthesis and Characterization of Carbon Skeleton

To form a first residue, a charge of 260 g potassium citrate wasincluded in a crucible and the crucible was placed into a quartz tubinginside a tubular furnace. A stream of argon gas was flowed into thefurnace and the furnace was heated at 5° C./min from room temperature(˜20-22° C.) to 600° C. The furnace was held at this temperature for 60minutes, followed by shutting-down the furnaces and removing the chargefrom the crucible after furnace cooling down, recovering 174.10 grams ofprocessed residue. To form second and third processed residues, the sameprocess described for the first residue was repeated for charges of 420and 974 grams of potassium citrate, separately. The resulting second andthird processed residues weighed 282.83 grams and 651.93 grams,respectively.

1108.9 grams from these three processed residues were combined togetherinto a crucible, which was placed into the quartz tubing inside thetubular furnace and a flow of argon gas was streamed into the furnace.The furnace was heated at 5° C./min to 800° C. The furnace was held at800° C. for 1 hour. The furnace was allowed to cool whereupon thecrucible was removed from the quartz tubing and thereafter 1085.74 gramsof a first final residue were recovered.

Following the same procedure described in this Example (800° C.), acharge of 120 grams of potassium residues introduced into the furnaceproduced about 77 grams of a second final residue (800° C.).

The combination of the first and second final residues resulted in about1,163 grams of a third final residue.

The 1,163 grams of third final residue was then mixed with 400 ml ofwater to form a slurry which was separated approximately equally intofour two-liter beakers. The pH of each slurry was measured to be greaterthan 13. Next, a concentrated hydrochloric acid solution was added toeach beaker with a violent evolution of carbon dioxide, which subsidedat a pH less than about 5. More hydrochloric acid solution was added toobtain a pH of about 1.9. Then the slurries were filtered and washed tofilter cakes that were dried in an oven at 120° C. for about 12 hours,followed by vacuum drying at 120° C. for 24 hours resulting in fourcarbon skeleton samples, a total of about 61.07 grams.

These carbon skeleton samples were characterized with SEM, XRD, Raman,BET/Pore-Size-Distributions. The SEM result for one carbon skeleton isshown FIG. 7. Surface morphologies of typical carbon skeleton particlesthat are prepared in the process described in this Example, hadsheet-like morphologies with their sheet edges being interconnected withsample thickness between 500 nm and 100 nm, and the sample width (orlength) being between 0.5 and 2 μm, therefore having an aspect ratio(defined as the ratio of the longest dimension of the sample width (orsheet length) to the sample thickness) ≥1, e.g., an aspect ratio ≥5 orgreater, or an aspect ratio ≥10.

X-Ray diffraction patterns of one carbon skeleton, shown in FIG. 8,shows that the carbon skeleton is substantially amorphous in phase.However, it does show a broad diffraction peak centered at around 20 ofabout 17°, indicating a d-spacing about 5.21 angstroms.

Raman scattering spectroscopy results for one carbon skeleton is shownin FIG. 9, showing Sp² carbon having a D-band at about 1365 cm⁻¹(Curve 1) and G-band at about 1589 cm⁻¹ (Curve 2) with a FWHM of 296 and96 cm⁻¹, respectively. Both D-band and G-band show a mixture of Gaussianand Lorentian distributions; D-band has about 33% Gaussian distributionsand G-band has about 61% Gaussian distributions. The ratio of the areafor D-band to the area for G-band is about 3.5.

BET surface area of one carbon skeleton was measured to be 1,205 m²/g bynitrogen absorption. The Incremental Pore Surface Area vs. the porewidth is plotted in FIG. 10A by using NLDFT method, showing a CumulativePore Surface Area of 1,515 m²/g. The discrepancy between BET surfacearea and NLDFT surface area may come from the fact that NLDFTdistributions are calculated with both nitrogen and CO₂ absorption data;CO₂ molecules may enter the pores smaller than those pores that nitrogenmolecules can enter. The NLDFT surface area in the pores peaked at 3.48angstrom is 443 m²/g, at 5.33 angstrom is 859 m²/g, and at 11.86angstrom (up to 20 angstroms) is 185 m²/g, a total of 1,502 m²/g for thepores of 20 angstroms or smaller, while the NLDFT surface area from thepores between 20 angstrom and 1000 angstrom is only 7.5 m²/g, and thesurface area from the pores of 20 angstroms or greater is only about0.5% of the total surface area.

The pore size distributions of the carbon skeleton sample weredetermined by nitrogen absorption and CO₂ absorption. The absorptionresults from nitrogen absorption and CO₂ absorption were combined toproduce the pore-size-distribution shown in FIG. 10B. The relationshipof Incremental Pore Volume (mL/g) vs. the pore width (angstrom) showsthat there are three major peaks located at 3.66 angstroms, 5.33angstroms, and 11.86 angstroms; the relationship of the Cumulative PoreVolume (mL/g) vs. pore width (angstrom) shows that there are about 0.080mL/g pores under the peak of 3.66 angstroms, about 0.240 mL/g poresunder the peak of 5.33 angstroms, about 0.108 mL/g pores under the peakof 11.86 angstroms, having 0.43 mL/g pores of 20 angstroms or smaller,0.042 mL/g pores between 20 and 100 angstroms, and a total of 0.572 mL/gpores of up to 1000 angstroms.

Example 10: Preparation and Characterization of Immobilized Selenium

Include 0.1206 grams of selenium (showing bulk properties of selenium)into a set of agate mortar and pestle and include 0.1206 grams of thecarbon skeleton that was prepared in accordance with Example 9 into thesame agate mortar and pestle. Manually grind the mixture of selenium andcarbon skeleton for about 30 minutes and transfer the ground mixture ofselenium and carbon skeleton into a stainless steel die (10 mm indiameter). Press the mixture in the die to a pressure of about 10 MPa toform a pellet of the mixture. Then, load the pellet into a sealedcontainer in the presence of an inert environment (argon) and place thesealed container containing the pellet into an oven. Heat the ovenincluding the sealed container containing the pellet to 240° C. (abovethe melting temperature of selenium) for, for example, 12 hours. Use,however, is envisioned of any combination of time and temperature, abovethe melting temperature of selenium, sufficient to cause the seleniumand carbon to react, either partially or fully react, and formimmobilized selenium having some or all of the features described inthis application. Next, unload the pellet from the container afterallowing the pellet to return to room temperature. The unloaded pelletis the immobilized selenium of this Example 10.

The immobilized selenium of this Example 10 was then characterized byTGA-DSC and TGA. TGA-DSC analysis results were collected for theimmobilized selenium under a stream of 200 ml/min of argon gas at aheating rate of 10° C./min. There is no observable endothermic DSC peakat temperatures near the melting point of selenium (about 230° C.),indicating that the immobilized selenium of this Example 10 is differentfrom the bulk-form of selenium molecules/atoms which should have amelting point at around 230° C. where there should be a endothermicpeak.

An investigation revealed that the TGA-DSC data may not be reliable whenthe heating temperature reaches a point where selenium molecules startto escape from the TGA-DSC sample crucible (graphite or ceramics). Tothis end, gas phase selenium molecules (from the sample crucible) enterthe argon carrier gas stream and appear to react with the TGA-DSCplatinum sample holder, which distorts the actual TGA-DSC thermochemicalbehaviors. The released selenium molecules from sample crucible reactingwith platinum sample holder, lead to a lower weight loss in thistemperature region. The selenium-platinum composite in the platinumsample holder is then released into the gas phase when the heatingtemperature reaches a point that is beyond 800° C. A complete seleniumrelease can occur at 1000° C. This investigation used up most of theimmobilized selenium sample of this Example 10. Therefore, a new sampleof the immobilized selenium (˜16 grams) was prepared using the sameprocess as was described in the earlier part of this Example 10.

The thermochemical behaviors of this new sample of immobilized seleniumwere studied by TGA analysis, which uses a ceramic sample holder thatcovers a very small thermocouple that is used for the TGA analysis. TheTGA analysis results for this new immobilized selenium sample are shownin FIG. 11A along with the TGA analysis results (FIG. 11B) forselenium-carbon composites (made with 50-50 Se-Super P carbon composite,and Se-Graphite (ground graphite), in the same process as preparation ofthe immobilized selenium of this Example 10. Super P is a commercialgrade carbon black widely used for lithium-ion battery industry. Groundgraphite was prepared by grinding Poco 2020 graphite. The TGA analysisdata are also summarized in the following Table 2.

TABLE 2 Immobilized Se in Example 10 Se-Graphite Se-Super P Temp. at theComp. Comp. bottom of the End Temp. Mid-Weight-Loss Temperature main wt.loss of TGA Expt. Mid-Wt.-Loss Temp, ° C. 471 480 595 660 1000Mid-Wt.-Loss Temp, K 744 753 868 933 1273 Kinetic Energy, Joule/Mole9,278 9,391 10,825 11,635 15,876

Immobilized selenium can have an initial weight loss temperaturestarting at about 400° C. vs. 340° C. for Se-Super P carbon compositeand the Se-Graphite carbon composite; a mid-point weight-losstemperature for immobilized selenium can be at about 595° C. vs. 480° C.for the Se-Super P composite and 471° C. for Se-Graphite composite; andmain weight loss completed at about 544° C. for Se-Super P composite andSe-Graphite composite, and 660° C. for the immobilized selenium. TheSe-Super P carbon composite and Se-Graphite carbon composite show lessthan 0.6% weight loss between 560° C. and 780° C., while immobilizedselenium shows a weight loss of about 2.5% from the bottom of the mainweight loss (˜660° C. to 1000° C.). These results suggest thatnon-immobilized selenium (Se-Super P carbon composite and Se-Graphitecomposite) has ≤1.2% of the total selenium which can escape from thecomposite at a temperature of ≥560° C., while the immobilized seleniumhas about 5.0% of the total selenium which can escape from carbonskeleton at a temperature of 660° C. The following details are providedto give examples that provide insight to the thermochemical behaviors.However, these details are not to be construed in a limiting sense.

Using the data of TGA mid-weight-loss temperature as examples ofthermochemical behaviors, as the heating temperature increases, thekinetic energy of the selenium molecules in Se-Super P composite andSe-Graphite composite increase to a level at which these seleniummolecules have enough energy to overcome the intermolecular interactionsamong selenium molecules and escape from liquid phase of the selenium.Herein Kinetic Energy=3RT/2, wherein: R is gas constant and T istemperature in Kelvin.

It was observed that the average kinetic energy of selenium moleculesfor Se-Super P composite was measured to be 9,391 joules/mole when theselenium molecules escape from the mixture of Se-Super P composite.However, the immobilized selenium needs to gain more energy to have anaverage kinetic energy of about 10,825 joules/mole for selenium to leavethe carbon skeleton to gas phase selenium molecules. It is believed thatthe selenium in immobilized selenium, either as an atomic form, as amolecular form, or as any form, may chemically interact with seleniumand the carbon skeleton beyond intermolecular interactions of selenium.In addition, the last portion of selenium that escapes from the carbonskeleton between 660° C. to 1000° C. has an average kinetic energy inthe range from 11,635 joules/mole to 15,876 joules/moles or more. Thissuggests that selenium in the immobilized selenium is more stable thanthe selenium in conventional selenium-carbon composites. The stabilizedselenium in the immobilized selenium of this Example 10 enhances theability of selenium, either as atomic forms, as molecular forms, or inany forms, to stay inside the carbon skeleton during electrochemicalprocesses, such as during charge and discharge cycling of a rechargeablebattery comprised of the immobilized selenium. In an example, this lastportion of selenium can require a kinetic energy of 11,635 joules/mole(≥660° C.) to escape the carbon skeleton and may be critical forselenium immobilization and may work as interfacial material betweencarbon skeleton and the majority of the immobilized selenium molecules.The portion of interfacial selenium in the immobilized selenium may be≥1.5%, ≥2.0%, ≥2.5%, or 3.0% of the total immobilized selenium.

FIG. 11A also shows the TGA studies of immobilized selenium with aheating rate of 16° C./min, having a temperature of 628° C. for themid-point-weight-loss of the contained selenium. As shown in FIG. 11C,for Se-Super P composite, the temperature at the mid-weight-loss of thecontained Se at a heating rate of 16° C./min is at 495° C. Withdifferent heating rates (e.g., 16° C./min, 10° C./min, 5° C./min, 2.5°C./min, and 1° C./min), activation energy and collision frequency may bedetermined and calculated using known methods, such as ASTM E1641-16 andE2958-14. The temperatures at 15% weight loss for different heatingrates are tabulated as shown in the following Table 3.

TABLE 3 Temperature (° C.) Immobilized Se Immobilized prepared by Seprepared the process by the process of Example of Example 10 Se-Super Pβ (° C./min) 10 (228-110) (155-82-2) Composite 16 590.65 570.13 471.0810 560.82 544.86 456.61 5 535.57 515.09 413.37 2.5 506.66 493.27 397.211 478.48 462.18 365.02 Activation Energy, 120.7 120.0 92.3 kJ/moleFrequency of Collisions 12.4 × 10⁵ 18.3 × 10⁵ 2.27 × 10⁵

The activation energy for selenium (non-immobilized or conventional) inthe Se-Super P composite was determined to be 92.3 kJ/mole with afrequency of collisions at 2.27×10⁵. The activation energy for seleniumin immobilized selenium (228-110 above) was also determined to be 120.7kJ/mole with a frequency of collisions at 12.4×10⁵. Another sample ofimmobilized selenium (155-82-2 above) that was prepared in the sameprocedures as Example 10 was also measured to have an activation energyof 120.0 kJ/mole and a frequency of collisions at 18.3×10⁵.

The kinetic rate constant for selenium is calculated using the Arrheniusequationk=Ae ^(−E) ^(a) ^(/RT)where k is the rate constant, E_(a) is the activation energy, A isfrequency of collisions, R is the gas constant, and T is the temperaturein Kelvin.

Referring to FIG. 11D, with above determined activation energy andcollision frequency, the kinetic rate constant was calculated using theArrhenius equation at different temperatures. FIG. 11D shows thatnon-immobilized selenium (Se-Super P composite-solid line) has muchhigher rate constant than that for immobilized selenium (228-110 (dottedline) and 115-82-2 (dashed line)), for example, about four orders ofmagnitude greater at 35° C. and about three orders of magnitude greaterat 100° C. In an example, at 50° C., the rate constant fornon-immobilized selenium (Super P) is 2.668×10⁻¹⁰ while immobilizedselenium has a rate constant at 7.26×10⁻¹⁴ (155-82-2) and 3.78×10⁻¹⁴(228-110). Selenium that has a lower kinetic rate constant has lesstendency to leave the host material (carbon), which may lead to betterbattery cycling performance.

FIG. 12 shows the spectrum of the immobilized selenium with Raman peaksof the D-band at 1368 cm⁻¹ and the G-band at 1596 cm⁻¹, having a ratioof the area for the D-band to the area for the G-band at 2.8. Ascompared to the Raman spectrum of the carbon skeleton shown in FIG. 9,selenium immobilization shifts both Raman peaks to a higher wavenumber,about 3 cm⁻¹ red shift for the D-band and 7 cm⁻¹ red shift for theG-band, which suggests that the bonding strength of Sp² carbon in thecarbon skeleton is being strengthened, with a red shift of about 4 cm⁻¹for the D-Band and a red shift of about 8 cm⁻¹ for the G-band. At thesame time, the ratio of the area for the D-band to the area for theG-band was also decreased from about 3.4 to 2.8, suggesting that eitherthe D-band gets relatively weaker or G-band gets relatively stronger. Astronger G-band may be desirable since the G-band can relate to a typeof carbon that allows the carbon skeleton to more readily conductelectrons, which can be desirable for electrochemical performances whenused in a rechargeable battery. Bulk or pure selenium typically shows asharp Raman shift peak at about 235 cm⁻¹. For immobilized selenium, theRaman spectrum in FIG. 12 shows a broad Raman peak at about 257 cm⁻¹(˜12.7% of the G-band in area) and a new broad hump at about 500 cm⁻¹(about 3.0% of the G-band area). It is believed that seleniumimmobilization changes Raman characteristics for both carbon skeletonand selenium, with all Raman peaks shifted to a higher wavenumber,suggesting that both of carbon-carbon Sp² bonds for the carbon skeletonand selenium-selenium bonds of the selenium are under compression.

The compression resulting from selenium immobilization strengthens bothcarbon-carbon Sp² bonds for carbon skeleton and Se—Se bonds forselenium, creating stronger selenium-selenium and carbon-seleniuminteractions. Therefore, more kinetic energy would be needed forselenium to overcome the stronger Se—Se bonding and strongercarbon-selenium interactions, which explains the observations in TGAanalysis of the immobilized selenium vs. Se-Super P composite andSe-Graphite composite.

Furthermore, under compression, the carbon skeleton would then have abetter capability of conducting electrons at the bonding level; andunder compression, selenium atoms or molecules would also have bettercapability of conducting electrons.

Stabilized selenium for the immobilized selenium along with enhancedelectron conductivity across the carbon skeleton and selenium can bedesirable in electrochemical processes, such as, for example, improvedspecific capacity for the active material with a minimum level ofshuttling, improved cycling capability due to the immobilization, acapability of being charged and discharged at a higher rate, etc.However, this is not to be construed in a limiting sense.

X-ray diffraction patterns for the immobilized selenium prepared inaccordance with Example 10, shown in FIG. 13, show a decrease in theintensity of the broad diffraction peak from the carbon skeleton with ad-spacing at about 5.21 angstroms—only about ⅓ the intensity, suggestingthat immobilized selenium further makes the carbon skeleton moredisordered, or causes more destruction to the order of the carbonskeleton. In an example, it is believed that this is because thecompression forces are applied on the carbon-carbon Sp² bonds.

FIG. 14 shows SEM image for the immobilized selenium that was preparedin accordance with Example 10, showing sheet-like morphologies, justlike the image in FIG. 7 for carbon skeleton. Though there is about 50%selenium that was immobilized in the carbon skeleton, there is noobservable selenium particles on the surfaces of the carbon skeleton,except that the inter-sheet connections have been destroyed, resultingin many flat sheets having high aspect ratios. These sheet-likemorphologies can be highly desirable for forming oriented coatingaligned along the flat-sheet directions, creating sheet surface tosurface contacts, leading to improved inter-sheet electricalconductivity, which may result in superior electrical performance forelectrochemical processes, such as in a rechargeable battery.

Example 11: Se Cathode Preparation

Into a mortar and pestle include 56 mg of the immobilized selenium thatwas prepared in accordance with Example 10; 7.04 mg of Super P; 182 μLof carboxymethyl cellulose (CMC) solution (which includes 1 mg of dryCMC for every 52 μL of CMC solution); 21.126 μL of SBR Latex dispersion(which contains 1 mg dry SBR Latex for every 6.036 μL SBR Latexdispersion); and 200 μL deionized water. Grind the particles, thebinders, and water manually into a slurry for 30 minutes to produce acathode slurry. The cathode slurry was then coated onto one-side of apiece of an electrically conductive substrate, e.g., a foil, andair-dried. In an example, the conductive substrate or foil can be analuminum (Al) foil. However this is not to be construed in a limitingsense since use of any suitable and/or desirable electrically conductivematerial of any shape or form, is envisioned. For the purpose ofdescription only, the use of Al foil to form a selenium cathode will bedescribed herein. However this is not to be construed in a limitingsense.

The slurry coated Al foil was then placed into a drying oven and heatedto a temperature of 55° C. for 12 hours, resulting in a selenium cathodecomprised of a dried sheet of immobilized selenium on one side of the Alfoil, with the other side of the Al foil being uncoated, i.e., barealuminum.

The selenium cathode was then punched to cathode discs, each having adiameter of 10 mm Some of these cathode discs were used as cathodes forrechargeable batteries.

Example 12: Li—Se Rechargeable Battery Assembly and Testing

The cathode discs from Example 11 were used to assemble Li—Serechargeable coil cell batteries in the manner described in the examplediscussed next and shown in FIG. 15. In this example, a 10 mm diametercathode disc 4 from Example 11 was placed onto a base 2 of a 2032stainless steel coin cell can which functions as the positive case ofthe coin cell (the “positive case” in FIG. 15) with the immobilizedselenium sheet 5 facing upward, away from base 2 of the positive caseand with the bare Al side facing and in-contact with the base 2 of thepositive case. Next, a battery separator 6 (19 mm in diameter and 25microns in thickness) was placed on top of the cathode disc 4 in contactwith the immobilized selenium sheet 5. In an example, the batteryseparator 6 can be an organic separator, or an inorganic separator, or asolid electrolyte separator. The organic separator can be a polymer, forexample, polyethylene, polypropylene, polyester, a halogenated polymer,a polyether, a polyketone, etc. The inorganic separator can be made fromglass and/or quartz fiber.

Next, 240 μL of electrolyte 7 comprising LiPF₆ (1M) in ethylenecarbonate (EC) and dimethyl carbonate (DMC) solvent (50-50 in weight)was introduced into the positive case 2 followed by placing a lithiumfoil disc 8 (15.6 mm in diameter and 250 microns in thickness) on a sideof the separator 6 opposite the cathode disc 4. Next, a stainless steel(SS) spacer 10 was placed on a side of the lithium foil disc 8 oppositethe separator 6 followed by placing one or more foam discs 12 made from,for example, nickel on a side of the SS spacer 10 opposite the lithiumfoil disc 8. The lithium foil 8, the SS spacer 10, and/or foam 12 diskcan function as an anode. Finally, a case 14 made from 2032 stainlesssteel 14, to function as the negative of the coin cell (the “negativecase” in FIG. 15), was placed on a side of the nickel foam disk(s) 12opposite the SS spacer 10 and on the rim of the positive case 2. Thepositive case 2 and the negative case 14 were then sealed together underhigh pressure, e.g., 1,000 psi. The sealing of the positive and negativecases (2, 14) under high pressure also had the effect of compressingtogether the stack comprising (from bottom to top in FIG. 15) thecathode disc 4, separator 6, lithium foil 8, SS spacer 10, and Ni foamdisc(s) 12. More than a dozen coin cell batteries were assembled usingthe battery separators described above and fiberglass separators. Theassembled coil cell batteries were then tested under followingconditions.

Some of the assembled coin cell batteries were tested undercharge-discharge rates of 0.1C and 1C by using a Lanhe Battery TesterCT2001A. Each coin cell battery was tested: (1) rest for 1 hour; (2)discharge to 1V; (3) rest for 10 minutes; (4) charge to 3V; (5) rest for10 minutes; repeat steps (2) to (5) for repeating cycling test.

FIG. 16A (left) shows the cycling test results (313 cycles at acharge-discharge rate of 0.1C) for a coin cell made in accordance withExample 12 using the cathode prepared in accordance with Example 11,showing excellent cycling stability, having a specific capacity of 633.7mAh/g after 313 cycles, which is a 93.4% retention of initial specificcapacity. The first discharge specific capacity was higher thanstoichiometric value, possibly due to some side reactions on the cathodeand anode surfaces. From the second cycle on, the specific capacitydecreased with cycling initially; however, the specific capacityincreased slightly from about 30 cycles to about 120 cycles beforestaying stable to about 180 cycles and then decreasing. FIG. 16B (right)also shows excellent cycling stability (100 cycles at 0.1C and then 500cycles at 1C) for another coin cell, having a specific capacity of 462.5mAh/g at the 600^(th) cycle, which is a 66.0% retention of the 2^(nd)cycle capacity at 0.1C or a 80.3% retention of the 105^(th) cyclecapacity at 1C. The Coulombic efficiency can be ≥95%, ≥98%, or as highas 100%, suggesting that there was no detectable amount of seleniumbeing shuttled between cathode and anode. This electrochemicalperformance is believed to be the results of the immobilized selenium inthe cathode, preventing selenium from being dissolved and shuttled fromcathode 14 to anode 2.

FIG. 17 shows cycling test results at different discharge-charge cyclingrates (between 0.1C and 10C-rate) for coin cell that was assembled witha polymer separator described in Example 12. The testing protocols weresimilar to the tests described above except for the cycling rates (0.1C,0.2C, 0.5C, 1C, 2C, 5C, and 10C); five cycles of charge and dischargewere performed for each C-Rate; then the cycling rate was returned to0.1C cycle. At the 0.1C rate, the battery exhibited a specific capacityaround stoichiometric value. In addition, the battery exhibited goodstability in cycling for cycling rates of 0.2C, 0.5C, 1C, and 2C. Thebattery also exhibited fast charging and discharging capability, cycled56% of stoichiometric capacity at 10C-rate, though showing a decliningspecific capacity along cycling. In other words at the 10C-rate thebattery took 3.3 minutes to charge and discharge to/from a capacity of56% of the stoichiometric value. Under such fast cycling rate, aconventional battery would not be expected to survive.

The Li—Se battery comprising immobilized selenium can recover itsspecific capacity to 670 mAh/g, 98% of its full capacity when cycled at0.1C-rate at the beginning of the test. It is believed that (1) thestabilization of selenium in the immobilized selenium cathode avoidsselenium from leaving the carbon skeleton, avoiding the selenium frombeing shuttled between the cathode and anode during cycling, whichenables the battery to have improved cycling performance; (2) both Sp²carbon-carbon bonds and carbon skeleton, selenium-selenium bonds, andcarbon-selenium interactions may be under compression, possiblyresulting in superior electrical conductivity within the carbonskeleton, within selenium particles, and among carbon and seleniuminterfaces, which may aid in achieving the observed cycling performanceat high C-rates.

The immobilized selenium body comprising selenium and carbon prepared inaccordance with the principles described herein can comprise one or moreof the following features:

(a) a kinetic energy required for a selenium particle to escape theimmobilized selenium can be ≥9.5 kJ/mole, ≥9.7 kJ/mole, ≥9.9 kJ/mole,≥10.1 kJ/mole, ≥10.3 kJ/mole, or ≥10.5 kJ/mole;

(b) a temperature required for a selenium particle to escape theimmobilized selenium can be can be ≥490° C., ≥500° C., ≥510° C., ≥520°C., ≥530° C., ≥540° C., ≥550° C., or ≥560° C.;

(c) the carbon can have a surface area (for pores less than 20angstroms) ≥500 m²/g, ≥600 m²/g, ≥700 m²/g, ≥800 m²/g, ≥900 m²/g, or≥1,000 m²/g;

(d) the carbon can have a surface area (for pores between 20 angstromsand 1000 angstroms) ≤20%, ≤15%, ≤10%, ≤5%, ≤3%, ≤2%, ≤1% of the totalsurface area;

(e) the carbon and/or selenium can be under compression. Benefits of theimmobilized selenium where the carbon and/or selenium are undercompression versus a carbon-selenium system where the carbon and/orselenium are not under compression can include: improved electron flow,reduced resistance to electron flow, or both, which can facilitateelectron delivery to the selenium and from selenium anions duringcharging and discharging of a rechargeable battery that has a cathodecomprised of the immobilized selenium;

(f) the immobilized selenium can comprise selenium that has anactivation energy higher than the activation energy higher forconventional (non-immobilized) selenium in order for the selenium toescape from the immobilized Se—C composite system. In an example, theactivation energy for non-immobilized selenium (Se-Super P compositesystem) was determined to be 92 kJ/mole, according to ASTM MethodE1641-16. In contrast, in an example, the activation energy for seleniumin the immobilized selenium comprising selenium and carbon can be ≥95kJ/mole, ≥98 kJ/mole, ≥101 kJ/mole, ≥104 kJ/mole, ≥107 kJ/mole, or ≥110kJ/mole. In another example, the activation energy for selenium in theimmobilized selenium comprising selenium and carbon can be ≥3%, ≥6%,≥9%, ≥12%, ≥15%, or ≥1.8% greater than that for selenium in Se-Super Pcomposite;

(g) the immobilized selenium can comprise selenium that has highercollision frequency than non-immobilized selenium. In an example, thecollision frequency for non-immobilized selenium was determined to be2.27×10⁵, according to the ATSM Method E1641-16. In contrast, in anexample, the collision frequency for selenium in immobilized selenium,comprising selenium and carbon, can be is ≥2.5×10⁵, ≥3.0×10⁵, ≥3.5×10⁵,≥4.0×10⁵, ≥4.5×10⁵, ≥5.0×10⁵, ≥5.5×10⁵, ≥6.0×10⁵, or ≥8.0×10⁵. Theimmobilized selenium can have a collision frequency ≥10%, 30%, ≥50%,≥80%, 100%, ≥130%, ≥150%, ≥180%, or ≥200% than for non-immobilizedselenium in an Se—C composite; and

(h) the immobilized selenium can comprise selenium that has a kineticrate constant that is ≤1/5, ≤1/10, ≤1/50, ≤1/100, ≤1/500, or ≤1/1000 ofthe kinetic rate constant for non-immobilized/conventional selenium. Inan example, the immobilized selenium can comprise selenium that has akinetic rate constant (at 50° C.) of ≤1×10⁻¹⁰, ≤5×10⁻¹¹, ≤1×10⁻¹¹,≤5×10⁻¹², or ≤5×10⁻¹³.

With the carbon and/or selenium of the immobilized selenium undercompression, the D-band and/or the G-band of Raman spectrum for the Sp²C—C bonds of the carbon (or carbon skeleton defined by said carbon) ofthe immobilized selenium can show a red (positive) shift, e.g., by ≥1cm⁻¹, ≥2 cm⁻¹, ≥3 cm⁻¹, ≥4 cm⁻¹, or ≥5 cm⁻¹ from a carbon feedstock.

With the carbon and/or selenium of the immobilized selenium undercompression, the selenium can have a red (positive) shift from the Ramanpeak of pure selenium (235 cm⁻¹), e.g., by ≥4 cm⁻¹, ≥6 cm⁻¹, ≥8 cm⁻¹,≥10 cm⁻¹, ≥12 cm⁻¹, ≥14 cm⁻¹, or ≥16 cm⁻¹, which red shift can suggestcompression on the selenium particles.

The immobilized selenium can be an elemental form of selenium and/or acompound form selenium.

The immobilized selenium comprising selenium and carbon can be alsodoped with one or more additional element(s) from Group 6 of thePeriodic Table (hereinafter, “additional G6 element(s)”), including, forexample, without limitation, sulfur and/or tellurium. The dopant levelmay range from as low as 100 ppm by weight to as high as 85% of thetotal weight of the immobilized selenium. In an example, the immobilizedselenium can comprise 15%-70% carbon and 30%-85% selenium and,optionally, additional G6 element(s). In an example, the immobilizedselenium can comprise (1) 15%-70% carbon and (2) 30%-85%selenium+additional G6 element(s) mixture. In the mixture comprisingselenium+additional G6 element(s), the additional G6 element(s) cancomprise between 0.1%-99% of the mixture and selenium can comprisebetween 1%-99.9% of the mixture. However, these ranges ofselenium+additional G6 element(s) are not to be construed in a limitingsense.

The immobilized selenium can include ≥5% selenium, ≥10% selenium, ≥20%selenium, ≥30%, ≥40% selenium, ≥50% selenium, ≥60% selenium, or ≥70% orhigher selenium.

The immobilized selenium can optionally including another element, suchas, for example, sulfur, tellurium, etc.

The immobilized selenium can be Raman-inactive or Raman-active. IfRaman-active, the immobilized selenium can have a Raman relative peakintensity at 255±25 cm¹, at 255±15 cm⁻¹, or at 255±10 cm⁻¹.

The immobilized selenium can comprise selenium having a Raman relativepeak intensity of ≥0.1%, ≥0.5%, ≥1%, ≥3%, or ≥5%, herein, the Ramanrelative peak intensity is defined as the area of the Raman peak at 255cm⁻¹ relative to the area of the D-band peak of the carbon Ramanspectrum.

The carbon comprising the immobilized selenium can serve as a carbonskeleton for selenium immobilization. The carbon skeleton can haveSp²-carbon-carbon bonds with a Raman D-band located at 1365±100 cm⁻¹ andG-band located at 1589±100 cm⁻¹; a D-band located at 1365±70 cm⁻¹ and aG-band located at 1589±70 cm⁻¹; a D-band located at 1365±50 cm⁻¹ and aG-band located at 1589±50 cm⁻¹; a D-band located at 1365±30 cm⁻¹ and aG-band located at 1589±30 cm⁻¹; or a D-band located at 1365±20 cm⁻¹ anda G-band located at 1589±20 cm⁻¹.

The carbon of the immobilized selenium can include Sp² carbon-carbonbonds, having Raman peaks featuring a D-band and a G-band. A ratio ofthe area of D-band to G-band can range from 0.01 to 100, from 0.1 to 50,or from 0.2 and 20.

The carbon of the immobilized selenium can include Sp² carbon-carbonbonds, having Raman peaks featuring a D-band and a G-band. Each of theD-band and the G-band can have a shift to a higher wavenumber ≥1 cm⁻¹,≥2 cm⁻¹, or more.

The carbon of the immobilized selenium can be doped with one or moreother elements in the period table.

The carbon of the immobilized selenium can be porous. The pore sizedistributions of the carbon skeleton can range between one angstrom to afew microns. The pore size distribution can have at least one peaklocated between one angstrom and 1000 angstroms, between one angstromand 100 angstroms, between one angstrom and 50 angstroms, between oneangstrom and 30 angstroms, or between one angstrom and 20 angstroms. Theporosity of the carbon skeleton can have pore size distributions withmore than one peak in the foregoing ranges.

The carbon of the immobilized selenium can include a pore volume between0.01 mL/g and 5 mL/g; between 0.01 mL/g and 3 mL/g; between 0.03 mL/gand 2.5 mL/g; or between 0.05 mL/g and 2.0 mL/g.

The carbon of the immobilized selenium can include a pore volume (thathas pore size <100 angstroms, <50 angstroms, <30 angstroms, or <20angstroms) that can be >30%, >40%, >50%, >60%, >70%, or >80% of thetotal measurable pore volume.

The carbon of the immobilized selenium can include a surface area >400m²/g, >500 m²/g, >600 m²/g, >700 m²/g, >800 m²/g, >900 m²/g, or >1000m²/g.

The carbon of the immobilized selenium can be amorphous and can have abroad peak centered at a d-spacing around 5.2 angstroms.

The carbon of the immobilized selenium can be of any morphology,platelet, sphere, fiber, needle, tubular, irregular, interconnected,agglomerated, discrete, or any solid particles. Platelet, fiber, needle,tubular, or some morphology having a certain level of aspect ratio maybe beneficial for achieving better inter-particle contact, resulting inenhanced electrical conductivity (over immobilized selenium made from adifferent aspect ratio), which may be beneficial to an electrochemicalcell, such as a rechargeable battery.

The carbon of the immobilized selenium can be of any particle size,having a median particle size between 1-9 nanometers and 2 millimeters,between 1-9 nanometers to <1000 microns, or between 20 nanometers to 100microns.

The selenium of the immobilized selenium can be amorphous, e.g., asdetermined by X-ray diffraction. The diffraction peak of the selenium ofthe immobilized selenium, which can have a d-spacing about 5.2 angstromsmay be weaker than the diffraction peak that for the carbon skeleton,e.g., 10% weaker, 20% weaker, 30% weaker, or 40% weaker.

In an example, a method of preparing the immobilized selenium caninclude:

(a) physical mixing carbon and selenium. The physical mixing can be byball-milling (dry and wet), mixing with mortar and pestle (dry or wet),jet-milling, horizontal milling, attrition milling, high shear mixing inslurries, regular slurry mixing with blade, etc.;

(b) the physically mixed carbon and selenium of step (a) can be heatedat the melting temperature of selenium or higher. The heating of thecarbon and selenium mixture can occur in the presence of an inert gasenvironment such as, but not limited to, argon, helium, nitrogen, etc.,or in an air or reactive environment;

(c) optionally homogenizing or blending the heated carbon and seleniumto achieve selenium immobilization; and

(d) cooling the immobilized selenium of step (c) to ambient or roomtemperature.

In another example, immobilized selenium can be prepared by dissolvingselenium onto carbon followed by evaporation. The solvent for dissolvingthe selenium can be an alcohol, an ether, an ester, a ketone, ahydrocarbon, a halogenated hydrocarbon, a nitrogen-containing compound,a phosphorus containing compound, a sulfur-containing compound, water,etc.

In another example, the immobilized selenium can be prepared by meltingselenium onto carbon, followed by removing extra or excessnon-immobilized selenium.

In an example, a method of making the immobilized selenium can include:

(a) mixing selenium and carbon together under dry or wet conditions;

(b) optional drying the mixture of step (a) at an elevated temperature;

(c) optional pelletizing the dried mixture of step (b);

(d) melting the selenium into the carbon to produce the immobilizedselenium.

Immobilized selenium can be used as a cathode material for arechargeable battery. The cathode can include an inorganic or an organicbinder. The inorganic binder can be a natural product, such as, forexample, CMC, or a synthetic product, such as, for example, SBR Rubberlatex. The cathode can include an optional electric-conductivitypromoter, such as, for example, graphite-derived small particles,graphene, carbon nano-tubes, carbon nano-sheet, carbon blacks, etc.Finally, the cathode can include a charge collector such as, forexample, an aluminum foil, a copper foil, a carbon foil, a carbonfabric, or other metallic foil.

The method of making the cathode can include coating an immobilizedselenium-containing slurry onto the charge collector, followed by dryingthe slurry coated charge collector (e.g., air dry, oven-dry, vacuumoven-dry, etc.). The immobilized selenium can be dispersed into theslurry, which can be prepared by a high shear mixer, a regular mixer, aplanetary mixer, a double-planetary mixer, a ball mill, a verticalattritor, a horizontal mill, etc. The slurry can then be coated onto thecharge collector, followed by drying in air or in vacuum. The coatedcathode can then be pressed or roller-milled (or calendared) prior toits use in a rechargeable battery.

A rechargeable battery can be made using the immobilized seleniumdescribed herein. The rechargeable battery can include a cathodecomprising the immobilized selenium, an anode, and a separatorseparating the anode and the cathode. The anode, the cathode, and theseparator can be immersed in an electrolyte, such as, for example,LiPF₆. The anode can be comprised of lithium, sodium, silicon, graphite,magnesium, tin, etc.

The separator can be comprised of an organic separator, an inorganicseparator, or a solid electrolyte separator. The organic separator cancomprise a polymer such as, for example, polyethylene, polypropylene,polyester, a halogenated polymer, a polyether, a polyketone, etc. Theinorganic separator can comprise a glass or quartz fiber, or a solidelectrolyte separator.

The electrolyte can comprise a lithium salt, a sodium salt, or othersalt from Group IA, IIA, and IIIA, in an organic solvent. The organicsolvent can comprise an organic carbonate compound, an ether, analcohol, an ester, a hydrocarbon, a halogenated hydrocarbon, a lithiumcontaining-solvent, etc.

The rechargeable battery can be used for electronics, an electric orhybrid vehicle, an industrial application, a military application, suchas a drone, an aerospace application, a marine application, etc.

The rechargeable battery can have an electrochemical capacity of ≥400mAh/g active amount of selenium, ≥450 mAh/g active amount of selenium,≥500 mAh/g active amount of selenium, ≥550 mAh/g active amount ofselenium, or ≥600 mAh/g active amount of selenium.

The rechargeable battery can undergo electrochemical cycling for ≥50cycles, ≥75 cycles, ≥100 cycles, ≥200 cycles, etc.

The rechargeable battery can be charged and/or discharged at 0.1C, 0.2C, 0.5C, 1C, 1.5 C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C or faster.

The rechargeable battery can retain a battery specificcapacity >30%, >40%, >50%, >60%, >70%, or >80% of the 2^(nd) dischargespecific capacity at a cycling rate of 0.1C after conducting high C-Ratecharge-discharge cycling (5 cycles at 0.1C, 5 cycles at 0.2C, 5 cyclesat 0.5C, 5 cycles at 1C, 5 cycles at 2C, 5 cycles at 5C, and 5 cycles at10C).

The rechargeable battery can have a Coulombic efficiency ≥50%, ≥60%,≥70%, ≥80%, ≥90%, or as high as around 100%.

Coloumbic efficiency of a battery is defined as follows:

$\eta_{c} = \begin{matrix}Q_{out} \\Q_{in}\end{matrix}$Where η_(c) is the Coloumbic efficiency (%)

Q_(out) is the amount of charge that exits the battery during adischarge cycle.

Q_(in) is the amount of charge that enters the battery during a chargingcycle.

The rechargeable battery can be charged at C-rate of 0.1C, 0.2 C, 0.5C,1C, 1.5 C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C or faster. A C-rate is ameasure of the rate at which a battery is discharged relative to itsmaximum capacity. For example, a 1C rate means that the dischargecurrent will discharge the entire battery in 1 hour. For example, for abattery with a capacity of 100 Amp-hrs, this equates to a dischargecurrent of 100 Amps A 5C rate for this same battery would be 500 Amps,and a 0.5C rate would be 50 Amps.

The cathode of the rechargeable battery can comprise one or moreelements of a chalcogen group such as selenium, sulfur, tellurium, andoxygen.

The anode of the rechargeable battery can comprise at least one elementof alkali metal, alkali earth metals, and group IIIA metals.

The separator of the rechargeable battery can comprise an organicseparator or an inorganic separator.

The electrolyte of the rechargeable battery can comprise at least oneelement of alkali metals, alkali earth metals, and Group IIIA metals;and a solvent of the electrolyte can comprise an organic solvent,carbonate-based, ether-based, or ester-based.

The rechargeable battery can have a specific capacity of ≥400 mAh/g,≥450 mAh/g, ≥500 mAh/g, ≥550 mAh/g, or ≥600 mAh/g.

The rechargeable battery can undergo electrochemical cycling for ≥50cycles, ≥75 cycles, ≥100 cycles, ≥200 cycles, etc.

The rechargeable battery can have a specificcapacity >30%, >40%, >50%, >60%, >70%, or >80% of the 2nd dischargespecific capacity at a cycling rate of 0.1C after conducting high C-Ratecharge-discharge cycling (5 cycles at 0.1C, 5 cycles at 0.2C, 5 cyclesat 0.5C, 5 cycles at 1C, 5 cycles at 2C, 5 cycles at 5C, and 5 cycles at10C).

The rechargeable battery can have has a Coulombic efficiency ≥50%, ≥60%,≥70%, ≥80%, or ≥90%.

Also disclosed is a composite comprising selenium and carbon, saidcomposite can have a platelet morphology with an aspect ratio of ≥1, ≥2,≥5, ≥10, or ≥20.

The selenium of the composite can be amorphous, e.g., as determined byX-ray diffraction. The diffraction peak of the selenium can have ad-spacing about 5.2 angstroms which may be weaker than that for a carbonskeleton, e.g., 10% weaker, 20% weaker, 30% weaker, or 40% weaker thanthe carbon skeleton.

In an example, the method of preparing the composite can include:

(a) physical mixing carbon and selenium. The physical mixing can be byball-milling (dry and wet), mixing with mortar and pestle (dry or wet),jet-milling, horizontal milling, attrition milling, high shear mixing inslurries, regular slurry mixing with blade, etc.;

(b) the physically mixed carbon and selenium of step (a) can be heatedto the melting temperature of selenium or higher and said heating canoccur in the presence of an inert gas environment such as, for example,argon, helium, nitrogen, etc., or in an air or reactive environment; and

(c) the heated carbon and selenium of step (b) can be homogenized orblended as an aid to achieving selenium immobilization.

In another example, the composite can be prepared by dissolving seleniumonto carbon followed by evaporation. The solvent for dissolving theselenium can include an alcohol, an ether, an ester, a ketone, ahydrocarbon, a halogenated hydrocarbon, a nitrogen-containing compound,a phosphorus containing compound, a sulfur-containing compound, water,etc.

The composite can be prepared by melting selenium onto (or into) carbon,followed by removing extra or excess non-immobilized selenium.

In an example, a method of making the composite can include:

(a) mixing selenium and carbon together under dry or wet conditions;

(b) optional drying the mixture of step (a) at an elevated temperature;

(c) optional pelletizing the dried mixture of step (b);

(d) melting the selenium into the carbon to produce the immobilizedselenium.

The composite can be used as a cathode material for a cathode of arechargeable battery. The cathode can include an inorganic or an organicbinder. The inorganic binder can be a natural product, such as, forexample, CMC, or a synthetic product, such as, for example, SBR Rubberlatex. The cathode can include an optional electric-conductivitypromoter, such as, for example, graphite-derived small particles,graphene, carbon nano-tubes, carbon nano-sheet, carbon blacks, etc.Finally, the cathode can include an electric charge collector such as,for example, an aluminum foil, a copper foil, a carbon foil, a carbonfabric, or other metallic foil.

The method of making the cathode can include coating an immobilizedselenium-containing slurry onto the charge collector, followed by dryingthe slurry coated charge collector (e.g., air dry, oven-dry, vacuumoven-dry, etc.). The immobilized selenium can be dispersed into theslurry, which can be prepared by a high shear mixer, a regular mixer, aplanetary mixer, a double-planetary mixer, a ball mill, a verticalattritor, a horizontal mill, etc. The slurry can then be coated onto thecharge collector, followed by drying in room air or in a vacuum. Thecoated cathode can then be pressed or roller-milled (or calendared)prior to its use in a rechargeable battery.

A rechargeable battery can be made using the above-described composite.The rechargeable battery can be charged at 0.1C, 0.2C, 0.5C, 1C, 1.5 C,2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C, 10C or faster.

Example 13: Preparation of Immobilized Selenium Doped with Sulfur,Electrode, and Batteries Thereof

Following the principles and procedures described in Example 10, 5atomic percent (at %) of selenium, 20 at % of selenium, 35 at % ofselenium, and 50 at % of selenium were separately replaced by sulfur inthe synthesis of immobilized sulfur-doped selenium detailed in thefollowing Table 4. Samples of the sulfur-doped immobilized selenium weresynthesized with the carbon skeleton prepared in accordance with theprinciples and procedures described Example 9.

TABLE 4 Sample ID Se, at % S, at % Se, wt % S, wt % Se95S5 95 5 97.9 2.1Se80S20 80 20 90.8 9.2 Se65S35 65 35 82.1 17.9 Se50S50 50 50 71.1 28.9

The thus prepared samples of immobilized sulfur-doped selenium were thenused to prepare a number of cathodes 4 comprising immobilizedsulfur-doped selenium in accordance with the principles and proceduresdescribed in Example 11 for immobilized selenium.

The thus prepared cathodes comprising immobilized sulfur-doped seleniumin this example were then used to prepare coin cell batteries inaccordance with the principles and procedures described in Example 12.

The assembled coin cell batteries in this example were then tested inthe battery tester described in Example 12, following the same testingprotocols also described in Example 12, at 0.1C and 1C charging anddischarging cycling rates.

The electrochemical cycling results at 0.1C for coil cell batteriesincluding a cathode comprised of immobilized sulfur-doped seleniumcathode made with immobilized sulfur-doped selenium sample (Se50S50 inTable 4) are shown in FIG. 18, having a 2^(nd) cycle discharge capacityof 821 mAh/g (which is considered good) and a steady Coulombicefficiency ≥95%, typically ≥98% (which is also considered good), or ashigh as 100%.

If selenium is assumed to have a stoichiometric specific capacity of 675mAh/g at the 0.1C cycling rate, then sulfur specific capacity would beestimated to be about 1,178 mAh/g (which is considered good for sulfur).The Coulombic efficiency ≥95%, ≥98%, or as high as 100% indicates thatthere is no significant amount of sulfur being shuttled between thecathode and anode. Sulfur species in the immobilized sulfur-dopedselenium battery function well in an electrolyte comprising carbonate.Typically, sulfur would not be expected to function well in a Li—Sbattery having carbonate as the electrolyte; a conventional Li—S batterytypically uses an ether-based electrolyte. Carbonate-based electrolyteis typically used in present lithium-ion batteries. Carbonate-basedelectrolyte is more economical and much more widely available in themarket place, as compared to ether-based electrolyte.

The electrochemical cycling results at the 1C cycling rate for coil cellbatteries including a cathode comprised of immobilized sulfur-dopedselenium cathode made with immobilized sulfur-doped selenium sample(Se50S50 in Table 4) are shown in FIG. 19, having a 2^(nd) cycledischarge capacity of 724 mAh/g and a steady Coulombic efficiency ≥95%,typically ≥98%, or as high as 100%.

If selenium is assumed to have a specific capacity of 625 mAh/g at the1C cycling rate, then the sulfur specific capacity would be estimated tobe about 966 mAh/g (which is also unexpected). Sulfur is an insulatorand has a very low electrical conductivity. Typically, a Li—S batterycannot cycle well at a fast cycling rate, such as at 1C rate.

As can be seen, when used as a cathode material in a rechargeablebattery, immobilized sulfur-doped selenium overcomes two fundamentalissues associated with Li—S batteries, namely, shuttling effect and lowcycling rate. With these two issues resolved, a battery including acathode comprised of immobilized sulfur-doped selenium can have highenergy density and high power density in real applications.

As can be seen, in an example, an immobilized sulfur-doped seleniumsystem or body can be formed by the method comprising: (a) mixingselenium, carbon, and sulfur to form a selenium-carbon-sulfur mixture;(b) heating the mixture of step (a) to a temperature above the meltingtemperature of selenium; and (c) causing the heated mixture of step (b)to cool to ambient or room temperature, thereby forming the immobilizedsulfur-doped selenium body.

The immobilized sulfur-doped selenium body of step (c) can compriseselenium and sulfur in a carbon skeleton body.

Step (a) can occur under a dry or a wet condition.

Step (b) can include homogenizing or blending the mixture.

Step (a) can include forming the selenium-carbon-sulfur mixture into abody. Step (b) can include heating the body to a temperature above themelting temperature of selenium. Step (c) can include causing orallowing the body to cool to ambient or room temperature.

Step (b) can include heating the mixture for a sufficient time for theselenium and carbon and sulfur to fully or partially react.

In another example, a method of preparing an immobilized sulfur-dopedselenium system or body can comprise: (a) forming a carbon skeleton; and(b) melting selenium and sulfur into the carbon skeleton.

In another example, a method of forming an immobilized sulfur-dopedselenium system or body can comprise: (a) mixing selenium and carbon andsulfur; and (b) following step (a), causing the selenium and sulfur todissolve onto the carbon thereby forming the immobilized sulfur-dopedselenium system or body.

A solvent for dissolving the selenium and sulfur can be an alcohol, anether, an ester, a ketone, a hydrocarbon, a halogenated hydrocarbon, anitrogen-containing compound, a phosphorus containing compound, asulfur-containing compound, or water. The solvent can be added to one ormore of the selenium, the sulfur, or the carbon prior to step (a),during step (a), or during step (b).

The method can further including (c) removing excess non-immobilizedselenium, non-immobilized sulfur, or both from the immobilizedsulfur-doped selenium system or body.

Also disclosed is a rechargeable battery comprising: a cathode comprisedof immobilized sulfur-doped selenium disposed on an electricallyconductive substrate; a separator disposed in direct contact with theelectrically conductive substrate, and in contact with the immobilizedsulfur-doped selenium; and an anode spaced from the cathode by theseparator.

The rechargeable battery can further include the anode spaced from theseparator by lithium. In an example, the lithium can be in the form of alithium foil.

The rechargeable battery can further include the cathode, the separator,the anode, and the lithium immersed in an electrolyte.

In the rechargeable battery the immobilized sulfur-doped selenium cancomprise a selenium-carbon-sulfur mixture, wherein the selenium andsulfur has been melted into the carbon.

In the rechargeable battery the separator can be formed from an organicmaterial, an inorganic material, or a solid electrolyte.

The rechargeable battery can have a Coulombic efficiency ≥95%.

The examples have been described with reference to the accompanyingfigures. Modifications and alterations will occur to others upon readingand understanding the foregoing examples. Accordingly, the foregoingexamples are not to be construed as limiting the disclosure.

The invention claimed is:
 1. A rechargeable battery comprising: acathode comprised of immobilized selenium disposed on an electricallyconductive substrate; a separator disposed in direct contact with theimmobilized selenium; and an anode, wherein the separator is formed froman organic material, an inorganic material, or a solid electrolyte; andthe immobilized selenium comprises a selenium-carbon mixture, whereinthe selenium has been melted into the carbon, thereby forming animmobilized selenium system or body comprising selenium in a carbonskeleton body, wherein an activation energy for a selenium particle toescape the immobilized selenium system or body is ≥95 kJ/mole, andwherein the immobilized selenium system or body has a mid-pointweight-loss temperature ≥520° C.
 2. A rechargeable battery comprising: acathode comprised of immobilized selenium disposed on an electricallyconductive substrate, the immobilized selenium exhibiting a mid-pointweight-loss temperature ≥520° C.; a separator disposed in direct contactwith the immobilized selenium; and an anode, wherein the separator isformed from an organic material, an inorganic material, or a solidelectrolyte.
 3. The rechargeable battery of claim 2, wherein therechargeable battery exhibits at least one of the following: anelectrochemical capacity of ≥400 mAh/g; a specific capacity of >30% of asecond discharge capacity at a charge-discharge cycling rate of 0.1 Cfollowing charge-discharge cycling at 5 cycles at 10 C; and a Coulombicefficiency ≥50%.
 4. The rechargeable battery of claim 2, wherein theanode is spaced from the separator by lithium.
 5. The rechargeablebattery of claim 4, wherein the cathode, the separator, the anode, andthe lithium are immersed in an electrolyte.